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+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
+ "http://www.w3.org/TR/html4/strict.dtd">
+<html>
+<head>
+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
+ <title>Source Level Debugging with LLVM</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+</head>
+<body>
+
+<div class="doc_title">Source Level Debugging with LLVM</div>
+
+<table class="layout" style="width:100%">
+ <tr class="layout">
+ <td class="left">
+<ul>
+ <li><a href="#introduction">Introduction</a>
+ <ol>
+ <li><a href="#phil">Philosophy behind LLVM debugging information</a></li>
+ <li><a href="#consumers">Debug information consumers</a></li>
+ <li><a href="#debugopt">Debugging optimized code</a></li>
+ </ol></li>
+ <li><a href="#format">Debugging information format</a>
+ <ol>
+ <li><a href="#debug_info_descriptors">Debug information descriptors</a>
+ <ul>
+ <li><a href="#format_compile_units">Compile unit descriptors</a></li>
+ <li><a href="#format_files">File descriptors</a></li>
+ <li><a href="#format_global_variables">Global variable descriptors</a></li>
+ <li><a href="#format_subprograms">Subprogram descriptors</a></li>
+ <li><a href="#format_blocks">Block descriptors</a></li>
+ <li><a href="#format_basic_type">Basic type descriptors</a></li>
+ <li><a href="#format_derived_type">Derived type descriptors</a></li>
+ <li><a href="#format_composite_type">Composite type descriptors</a></li>
+ <li><a href="#format_subrange">Subrange descriptors</a></li>
+ <li><a href="#format_enumeration">Enumerator descriptors</a></li>
+ <li><a href="#format_variables">Local variables</a></li>
+ </ul></li>
+ <li><a href="#format_common_intrinsics">Debugger intrinsic functions</a>
+ <ul>
+ <li><a href="#format_common_declare">llvm.dbg.declare</a></li>
+ <li><a href="#format_common_value">llvm.dbg.value</a></li>
+ </ul></li>
+ </ol></li>
+ <li><a href="#format_common_lifetime">Object lifetimes and scoping</a></li>
+ <li><a href="#ccxx_frontend">C/C++ front-end specific debug information</a>
+ <ol>
+ <li><a href="#ccxx_compile_units">C/C++ source file information</a></li>
+ <li><a href="#ccxx_global_variable">C/C++ global variable information</a></li>
+ <li><a href="#ccxx_subprogram">C/C++ function information</a></li>
+ <li><a href="#ccxx_basic_types">C/C++ basic types</a></li>
+ <li><a href="#ccxx_derived_types">C/C++ derived types</a></li>
+ <li><a href="#ccxx_composite_types">C/C++ struct/union types</a></li>
+ <li><a href="#ccxx_enumeration_types">C/C++ enumeration types</a></li>
+ </ol></li>
+</ul>
+</td>
+<td class="right">
+<img src="img/venusflytrap.jpg" alt="A leafy and green bug eater" width="247"
+height="369">
+</td>
+</tr></table>
+
+<div class="doc_author">
+ <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>
+ and <a href="mailto:jlaskey@mac.com">Jim Laskey</a></p>
+</div>
+
+
+<!-- *********************************************************************** -->
+<div class="doc_section"><a name="introduction">Introduction</a></div>
+<!-- *********************************************************************** -->
+
+<div class="doc_text">
+
+<p>This document is the central repository for all information pertaining to
+ debug information in LLVM. It describes the <a href="#format">actual format
+ that the LLVM debug information</a> takes, which is useful for those
+ interested in creating front-ends or dealing directly with the information.
+ Further, this document provides specific examples of what debug information
+ for C/C++.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="phil">Philosophy behind LLVM debugging information</a>
+</div>
+
+<div class="doc_text">
+
+<p>The idea of the LLVM debugging information is to capture how the important
+ pieces of the source-language's Abstract Syntax Tree map onto LLVM code.
+ Several design aspects have shaped the solution that appears here. The
+ important ones are:</p>
+
+<ul>
+ <li>Debugging information should have very little impact on the rest of the
+ compiler. No transformations, analyses, or code generators should need to
+ be modified because of debugging information.</li>
+
+ <li>LLVM optimizations should interact in <a href="#debugopt">well-defined and
+ easily described ways</a> with the debugging information.</li>
+
+ <li>Because LLVM is designed to support arbitrary programming languages,
+ LLVM-to-LLVM tools should not need to know anything about the semantics of
+ the source-level-language.</li>
+
+ <li>Source-level languages are often <b>widely</b> different from one another.
+ LLVM should not put any restrictions of the flavor of the source-language,
+ and the debugging information should work with any language.</li>
+
+ <li>With code generator support, it should be possible to use an LLVM compiler
+ to compile a program to native machine code and standard debugging
+ formats. This allows compatibility with traditional machine-code level
+ debuggers, like GDB or DBX.</li>
+</ul>
+
+<p>The approach used by the LLVM implementation is to use a small set
+ of <a href="#format_common_intrinsics">intrinsic functions</a> to define a
+ mapping between LLVM program objects and the source-level objects. The
+ description of the source-level program is maintained in LLVM metadata
+ in an <a href="#ccxx_frontend">implementation-defined format</a>
+ (the C/C++ front-end currently uses working draft 7 of
+ the <a href="http://www.eagercon.com/dwarf/dwarf3std.htm">DWARF 3
+ standard</a>).</p>
+
+<p>When a program is being debugged, a debugger interacts with the user and
+ turns the stored debug information into source-language specific information.
+ As such, a debugger must be aware of the source-language, and is thus tied to
+ a specific language or family of languages.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="consumers">Debug information consumers</a>
+</div>
+
+<div class="doc_text">
+
+<p>The role of debug information is to provide meta information normally
+ stripped away during the compilation process. This meta information provides
+ an LLVM user a relationship between generated code and the original program
+ source code.</p>
+
+<p>Currently, debug information is consumed by DwarfDebug to produce dwarf
+ information used by the gdb debugger. Other targets could use the same
+ information to produce stabs or other debug forms.</p>
+
+<p>It would also be reasonable to use debug information to feed profiling tools
+ for analysis of generated code, or, tools for reconstructing the original
+ source from generated code.</p>
+
+<p>TODO - expound a bit more.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="debugopt">Debugging optimized code</a>
+</div>
+
+<div class="doc_text">
+
+<p>An extremely high priority of LLVM debugging information is to make it
+ interact well with optimizations and analysis. In particular, the LLVM debug
+ information provides the following guarantees:</p>
+
+<ul>
+ <li>LLVM debug information <b>always provides information to accurately read
+ the source-level state of the program</b>, regardless of which LLVM
+ optimizations have been run, and without any modification to the
+ optimizations themselves. However, some optimizations may impact the
+ ability to modify the current state of the program with a debugger, such
+ as setting program variables, or calling functions that have been
+ deleted.</li>
+
+ <li>LLVM optimizations gracefully interact with debugging information. If
+ they are not aware of debug information, they are automatically disabled
+ as necessary in the cases that would invalidate the debug info. This
+ retains the LLVM features, making it easy to write new
+ transformations.</li>
+
+ <li>As desired, LLVM optimizations can be upgraded to be aware of the LLVM
+ debugging information, allowing them to update the debugging information
+ as they perform aggressive optimizations. This means that, with effort,
+ the LLVM optimizers could optimize debug code just as well as non-debug
+ code.</li>
+
+ <li>LLVM debug information does not prevent many important optimizations from
+ happening (for example inlining, basic block reordering/merging/cleanup,
+ tail duplication, etc), further reducing the amount of the compiler that
+ eventually is "aware" of debugging information.</li>
+
+ <li>LLVM debug information is automatically optimized along with the rest of
+ the program, using existing facilities. For example, duplicate
+ information is automatically merged by the linker, and unused information
+ is automatically removed.</li>
+</ul>
+
+<p>Basically, the debug information allows you to compile a program with
+ "<tt>-O0 -g</tt>" and get full debug information, allowing you to arbitrarily
+ modify the program as it executes from a debugger. Compiling a program with
+ "<tt>-O3 -g</tt>" gives you full debug information that is always available
+ and accurate for reading (e.g., you get accurate stack traces despite tail
+ call elimination and inlining), but you might lose the ability to modify the
+ program and call functions where were optimized out of the program, or
+ inlined away completely.</p>
+
+<p><a href="TestingGuide.html#quicktestsuite">LLVM test suite</a> provides a
+ framework to test optimizer's handling of debugging information. It can be
+ run like this:</p>
+
+<div class="doc_code">
+<pre>
+% cd llvm/projects/test-suite/MultiSource/Benchmarks # or some other level
+% make TEST=dbgopt
+</pre>
+</div>
+
+<p>This will test impact of debugging information on optimization passes. If
+ debugging information influences optimization passes then it will be reported
+ as a failure. See <a href="TestingGuide.html">TestingGuide</a> for more
+ information on LLVM test infrastructure and how to run various tests.</p>
+
+</div>
+
+<!-- *********************************************************************** -->
+<div class="doc_section">
+ <a name="format">Debugging information format</a>
+</div>
+<!-- *********************************************************************** -->
+
+<div class="doc_text">
+
+<p>LLVM debugging information has been carefully designed to make it possible
+ for the optimizer to optimize the program and debugging information without
+ necessarily having to know anything about debugging information. In
+ particular, the use of metadata avoids duplicated debugging information from
+ the beginning, and the global dead code elimination pass automatically
+ deletes debugging information for a function if it decides to delete the
+ function. </p>
+
+<p>To do this, most of the debugging information (descriptors for types,
+ variables, functions, source files, etc) is inserted by the language
+ front-end in the form of LLVM metadata. </p>
+
+<p>Debug information is designed to be agnostic about the target debugger and
+ debugging information representation (e.g. DWARF/Stabs/etc). It uses a
+ generic pass to decode the information that represents variables, types,
+ functions, namespaces, etc: this allows for arbitrary source-language
+ semantics and type-systems to be used, as long as there is a module
+ written for the target debugger to interpret the information. </p>
+
+<p>To provide basic functionality, the LLVM debugger does have to make some
+ assumptions about the source-level language being debugged, though it keeps
+ these to a minimum. The only common features that the LLVM debugger assumes
+ exist are <a href="#format_files">source files</a>,
+ and <a href="#format_global_variables">program objects</a>. These abstract
+ objects are used by a debugger to form stack traces, show information about
+ local variables, etc.</p>
+
+<p>This section of the documentation first describes the representation aspects
+ common to any source-language. The <a href="#ccxx_frontend">next section</a>
+ describes the data layout conventions used by the C and C++ front-ends.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="debug_info_descriptors">Debug information descriptors</a>
+</div>
+
+<div class="doc_text">
+
+<p>In consideration of the complexity and volume of debug information, LLVM
+ provides a specification for well formed debug descriptors. </p>
+
+<p>Consumers of LLVM debug information expect the descriptors for program
+ objects to start in a canonical format, but the descriptors can include
+ additional information appended at the end that is source-language
+ specific. All LLVM debugging information is versioned, allowing backwards
+ compatibility in the case that the core structures need to change in some
+ way. Also, all debugging information objects start with a tag to indicate
+ what type of object it is. The source-language is allowed to define its own
+ objects, by using unreserved tag numbers. We recommend using with tags in
+ the range 0x1000 through 0x2000 (there is a defined enum DW_TAG_user_base =
+ 0x1000.)</p>
+
+<p>The fields of debug descriptors used internally by LLVM
+ are restricted to only the simple data types <tt>i32</tt>, <tt>i1</tt>,
+ <tt>float</tt>, <tt>double</tt>, <tt>mdstring</tt> and <tt>mdnode</tt>. </p>
+
+<div class="doc_code">
+<pre>
+!1 = metadata !{
+ i32, ;; A tag
+ ...
+}
+</pre>
+</div>
+
+<p><a name="LLVMDebugVersion">The first field of a descriptor is always an
+ <tt>i32</tt> containing a tag value identifying the content of the
+ descriptor. The remaining fields are specific to the descriptor. The values
+ of tags are loosely bound to the tag values of DWARF information entries.
+ However, that does not restrict the use of the information supplied to DWARF
+ targets. To facilitate versioning of debug information, the tag is augmented
+ with the current debug version (LLVMDebugVersion = 8 &lt;&lt; 16 or 0x80000 or
+ 524288.)</a></p>
+
+<p>The details of the various descriptors follow.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="format_compile_units">Compile unit descriptors</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!0 = metadata !{
+ i32, ;; Tag = 17 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
+ ;; (DW_TAG_compile_unit)
+ i32, ;; Unused field.
+ i32, ;; DWARF language identifier (ex. DW_LANG_C89)
+ metadata, ;; Source file name
+ metadata, ;; Source file directory (includes trailing slash)
+ metadata ;; Producer (ex. "4.0.1 LLVM (LLVM research group)")
+ i1, ;; True if this is a main compile unit.
+ i1, ;; True if this is optimized.
+ metadata, ;; Flags
+ i32 ;; Runtime version
+}
+</pre>
+</div>
+
+<p>These descriptors contain a source language ID for the file (we use the DWARF
+ 3.0 ID numbers, such as <tt>DW_LANG_C89</tt>, <tt>DW_LANG_C_plus_plus</tt>,
+ <tt>DW_LANG_Cobol74</tt>, etc), three strings describing the filename,
+ working directory of the compiler, and an identifier string for the compiler
+ that produced it.</p>
+
+<p>Compile unit descriptors provide the root context for objects declared in a
+ specific compilation unit. File descriptors are defined using this context.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="format_files">File descriptors</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!0 = metadata !{
+ i32, ;; Tag = 41 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
+ ;; (DW_TAG_file_type)
+ metadata, ;; Source file name
+ metadata, ;; Source file directory (includes trailing slash)
+ metadata ;; Reference to compile unit where defined
+}
+</pre>
+</div>
+
+<p>These descriptors contain information for a file. Global variables and top
+ level functions would be defined using this context.k File descriptors also
+ provide context for source line correspondence. </p>
+
+<p>Each input file is encoded as a separate file descriptor in LLVM debugging
+ information output. Each file descriptor would be defined using a
+ compile unit. </p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="format_global_variables">Global variable descriptors</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!1 = metadata !{
+ i32, ;; Tag = 52 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
+ ;; (DW_TAG_variable)
+ i32, ;; Unused field.
+ metadata, ;; Reference to context descriptor
+ metadata, ;; Name
+ metadata, ;; Display name (fully qualified C++ name)
+ metadata, ;; MIPS linkage name (for C++)
+ metadata, ;; Reference to file where defined
+ i32, ;; Line number where defined
+ metadata, ;; Reference to type descriptor
+ i1, ;; True if the global is local to compile unit (static)
+ i1, ;; True if the global is defined in the compile unit (not extern)
+ { }* ;; Reference to the global variable
+}
+</pre>
+</div>
+
+<p>These descriptors provide debug information about globals variables. The
+provide details such as name, type and where the variable is defined.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="format_subprograms">Subprogram descriptors</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32, ;; Tag = 46 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
+ ;; (DW_TAG_subprogram)
+ i32, ;; Unused field.
+ metadata, ;; Reference to context descriptor
+ metadata, ;; Name
+ metadata, ;; Display name (fully qualified C++ name)
+ metadata, ;; MIPS linkage name (for C++)
+ metadata, ;; Reference to file where defined
+ i32, ;; Line number where defined
+ metadata, ;; Reference to type descriptor
+ i1, ;; True if the global is local to compile unit (static)
+ i1 ;; True if the global is defined in the compile unit (not extern)
+}
+</pre>
+</div>
+
+<p>These descriptors provide debug information about functions, methods and
+ subprograms. They provide details such as name, return types and the source
+ location where the subprogram is defined.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="format_blocks">Block descriptors</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!3 = metadata !{
+ i32, ;; Tag = 13 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_lexical_block)
+ metadata ;; Reference to context descriptor
+}
+</pre>
+</div>
+
+<p>These descriptors provide debug information about nested blocks within a
+ subprogram. The array of member descriptors is used to define local
+ variables and deeper nested blocks.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="format_basic_type">Basic type descriptors</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!4 = metadata !{
+ i32, ;; Tag = 36 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
+ ;; (DW_TAG_base_type)
+ metadata, ;; Reference to context (typically a compile unit)
+ metadata, ;; Name (may be "" for anonymous types)
+ metadata, ;; Reference to file where defined (may be NULL)
+ i32, ;; Line number where defined (may be 0)
+ i64, ;; Size in bits
+ i64, ;; Alignment in bits
+ i64, ;; Offset in bits
+ i32, ;; Flags
+ i32 ;; DWARF type encoding
+}
+</pre>
+</div>
+
+<p>These descriptors define primitive types used in the code. Example int, bool
+ and float. The context provides the scope of the type, which is usually the
+ top level. Since basic types are not usually user defined the compile unit
+ and line number can be left as NULL and 0. The size, alignment and offset
+ are expressed in bits and can be 64 bit values. The alignment is used to
+ round the offset when embedded in a
+ <a href="#format_composite_type">composite type</a> (example to keep float
+ doubles on 64 bit boundaries.) The offset is the bit offset if embedded in
+ a <a href="#format_composite_type">composite type</a>.</p>
+
+<p>The type encoding provides the details of the type. The values are typically
+ one of the following:</p>
+
+<div class="doc_code">
+<pre>
+DW_ATE_address = 1
+DW_ATE_boolean = 2
+DW_ATE_float = 4
+DW_ATE_signed = 5
+DW_ATE_signed_char = 6
+DW_ATE_unsigned = 7
+DW_ATE_unsigned_char = 8
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="format_derived_type">Derived type descriptors</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!5 = metadata !{
+ i32, ;; Tag (see below)
+ metadata, ;; Reference to context
+ metadata, ;; Name (may be "" for anonymous types)
+ metadata, ;; Reference to file where defined (may be NULL)
+ i32, ;; Line number where defined (may be 0)
+ i32, ;; Size in bits
+ i32, ;; Alignment in bits
+ i32, ;; Offset in bits
+ metadata ;; Reference to type derived from
+}
+</pre>
+</div>
+
+<p>These descriptors are used to define types derived from other types. The
+value of the tag varies depending on the meaning. The following are possible
+tag values:</p>
+
+<div class="doc_code">
+<pre>
+DW_TAG_formal_parameter = 5
+DW_TAG_member = 13
+DW_TAG_pointer_type = 15
+DW_TAG_reference_type = 16
+DW_TAG_typedef = 22
+DW_TAG_const_type = 38
+DW_TAG_volatile_type = 53
+DW_TAG_restrict_type = 55
+</pre>
+</div>
+
+<p><tt>DW_TAG_member</tt> is used to define a member of
+ a <a href="#format_composite_type">composite type</a>
+ or <a href="#format_subprograms">subprogram</a>. The type of the member is
+ the <a href="#format_derived_type">derived
+ type</a>. <tt>DW_TAG_formal_parameter</tt> is used to define a member which
+ is a formal argument of a subprogram.</p>
+
+<p><tt>DW_TAG_typedef</tt> is used to provide a name for the derived type.</p>
+
+<p><tt>DW_TAG_pointer_type</tt>,<tt>DW_TAG_reference_type</tt>,
+ <tt>DW_TAG_const_type</tt>, <tt>DW_TAG_volatile_type</tt>
+ and <tt>DW_TAG_restrict_type</tt> are used to qualify
+ the <a href="#format_derived_type">derived type</a>. </p>
+
+<p><a href="#format_derived_type">Derived type</a> location can be determined
+ from the compile unit and line number. The size, alignment and offset are
+ expressed in bits and can be 64 bit values. The alignment is used to round
+ the offset when embedded in a <a href="#format_composite_type">composite
+ type</a> (example to keep float doubles on 64 bit boundaries.) The offset is
+ the bit offset if embedded in a <a href="#format_composite_type">composite
+ type</a>.</p>
+
+<p>Note that the <tt>void *</tt> type is expressed as a
+ <tt>llvm.dbg.derivedtype.type</tt> with tag of <tt>DW_TAG_pointer_type</tt>
+ and <tt>NULL</tt> derived type.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="format_composite_type">Composite type descriptors</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!6 = metadata !{
+ i32, ;; Tag (see below)
+ metadata, ;; Reference to context
+ metadata, ;; Name (may be "" for anonymous types)
+ metadata, ;; Reference to file where defined (may be NULL)
+ i32, ;; Line number where defined (may be 0)
+ i64, ;; Size in bits
+ i64, ;; Alignment in bits
+ i64, ;; Offset in bits
+ i32, ;; Flags
+ metadata, ;; Reference to type derived from
+ metadata, ;; Reference to array of member descriptors
+ i32 ;; Runtime languages
+}
+</pre>
+</div>
+
+<p>These descriptors are used to define types that are composed of 0 or more
+elements. The value of the tag varies depending on the meaning. The following
+are possible tag values:</p>
+
+<div class="doc_code">
+<pre>
+DW_TAG_array_type = 1
+DW_TAG_enumeration_type = 4
+DW_TAG_structure_type = 19
+DW_TAG_union_type = 23
+DW_TAG_vector_type = 259
+DW_TAG_subroutine_type = 21
+DW_TAG_inheritance = 28
+</pre>
+</div>
+
+<p>The vector flag indicates that an array type is a native packed vector.</p>
+
+<p>The members of array types (tag = <tt>DW_TAG_array_type</tt>) or vector types
+ (tag = <tt>DW_TAG_vector_type</tt>) are <a href="#format_subrange">subrange
+ descriptors</a>, each representing the range of subscripts at that level of
+ indexing.</p>
+
+<p>The members of enumeration types (tag = <tt>DW_TAG_enumeration_type</tt>) are
+ <a href="#format_enumeration">enumerator descriptors</a>, each representing
+ the definition of enumeration value for the set.</p>
+
+<p>The members of structure (tag = <tt>DW_TAG_structure_type</tt>) or union (tag
+ = <tt>DW_TAG_union_type</tt>) types are any one of
+ the <a href="#format_basic_type">basic</a>,
+ <a href="#format_derived_type">derived</a>
+ or <a href="#format_composite_type">composite</a> type descriptors, each
+ representing a field member of the structure or union.</p>
+
+<p>For C++ classes (tag = <tt>DW_TAG_structure_type</tt>), member descriptors
+ provide information about base classes, static members and member
+ functions. If a member is a <a href="#format_derived_type">derived type
+ descriptor</a> and has a tag of <tt>DW_TAG_inheritance</tt>, then the type
+ represents a base class. If the member of is
+ a <a href="#format_global_variables">global variable descriptor</a> then it
+ represents a static member. And, if the member is
+ a <a href="#format_subprograms">subprogram descriptor</a> then it represents
+ a member function. For static members and member
+ functions, <tt>getName()</tt> returns the members link or the C++ mangled
+ name. <tt>getDisplayName()</tt> the simplied version of the name.</p>
+
+<p>The first member of subroutine (tag = <tt>DW_TAG_subroutine_type</tt>) type
+ elements is the return type for the subroutine. The remaining elements are
+ the formal arguments to the subroutine.</p>
+
+<p><a href="#format_composite_type">Composite type</a> location can be
+ determined from the compile unit and line number. The size, alignment and
+ offset are expressed in bits and can be 64 bit values. The alignment is used
+ to round the offset when embedded in
+ a <a href="#format_composite_type">composite type</a> (as an example, to keep
+ float doubles on 64 bit boundaries.) The offset is the bit offset if embedded
+ in a <a href="#format_composite_type">composite type</a>.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="format_subrange">Subrange descriptors</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+%<a href="#format_subrange">llvm.dbg.subrange.type</a> = type {
+ i32, ;; Tag = 33 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_subrange_type)
+ i64, ;; Low value
+ i64 ;; High value
+}
+</pre>
+</div>
+
+<p>These descriptors are used to define ranges of array subscripts for an array
+ <a href="#format_composite_type">composite type</a>. The low value defines
+ the lower bounds typically zero for C/C++. The high value is the upper
+ bounds. Values are 64 bit. High - low + 1 is the size of the array. If low
+ == high the array will be unbounded.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="format_enumeration">Enumerator descriptors</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!6 = metadata !{
+ i32, ;; Tag = 40 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
+ ;; (DW_TAG_enumerator)
+ metadata, ;; Name
+ i64 ;; Value
+}
+</pre>
+</div>
+
+<p>These descriptors are used to define members of an
+ enumeration <a href="#format_composite_type">composite type</a>, it
+ associates the name to the value.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="format_variables">Local variables</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!7 = metadata !{
+ i32, ;; Tag (see below)
+ metadata, ;; Context
+ metadata, ;; Name
+ metadata, ;; Reference to file where defined
+ i32, ;; Line number where defined
+ metadata ;; Type descriptor
+}
+</pre>
+</div>
+
+<p>These descriptors are used to define variables local to a sub program. The
+ value of the tag depends on the usage of the variable:</p>
+
+<div class="doc_code">
+<pre>
+DW_TAG_auto_variable = 256
+DW_TAG_arg_variable = 257
+DW_TAG_return_variable = 258
+</pre>
+</div>
+
+<p>An auto variable is any variable declared in the body of the function. An
+ argument variable is any variable that appears as a formal argument to the
+ function. A return variable is used to track the result of a function and
+ has no source correspondent.</p>
+
+<p>The context is either the subprogram or block where the variable is defined.
+ Name the source variable name. Compile unit and line indicate where the
+ variable was defined. Type descriptor defines the declared type of the
+ variable.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="format_common_intrinsics">Debugger intrinsic functions</a>
+</div>
+
+<div class="doc_text">
+
+<p>LLVM uses several intrinsic functions (name prefixed with "llvm.dbg") to
+ provide debug information at various points in generated code.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="format_common_declare">llvm.dbg.declare</a>
+</div>
+
+<div class="doc_text">
+<pre>
+ void %<a href="#format_common_declare">llvm.dbg.declare</a>( { } *, metadata )
+</pre>
+
+<p>This intrinsic provides information about a local element (ex. variable.) The
+ first argument is the alloca for the variable, cast to a <tt>{ }*</tt>. The
+ second argument is
+ the <tt>%<a href="#format_variables">llvm.dbg.variable</a></tt> containing
+ the description of the variable. </p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="format_common_value">llvm.dbg.value</a>
+</div>
+
+<div class="doc_text">
+<pre>
+ void %<a href="#format_common_value">llvm.dbg.value</a>( metadata, i64, metadata )
+</pre>
+
+<p>This intrinsic provides information when a user source variable is set to a
+ new value. The first argument is the new value (wrapped as metadata). The
+ second argument is the offset in the user source variable where the new value
+ is written. The third argument is
+ the <tt>%<a href="#format_variables">llvm.dbg.variable</a></tt> containing
+ the description of the user source variable. </p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="format_common_lifetime">Object lifetimes and scoping</a>
+</div>
+
+<div class="doc_text">
+<p>In many languages, the local variables in functions can have their lifetimes
+ or scopes limited to a subset of a function. In the C family of languages,
+ for example, variables are only live (readable and writable) within the
+ source block that they are defined in. In functional languages, values are
+ only readable after they have been defined. Though this is a very obvious
+ concept, it is non-trivial to model in LLVM, because it has no notion of
+ scoping in this sense, and does not want to be tied to a language's scoping
+ rules.</p>
+
+<p>In order to handle this, the LLVM debug format uses the metadata attached to
+ llvm instructions to encode line number and scoping information. Consider
+ the following C fragment, for example:</p>
+
+<div class="doc_code">
+<pre>
+1. void foo() {
+2. int X = 21;
+3. int Y = 22;
+4. {
+5. int Z = 23;
+6. Z = X;
+7. }
+8. X = Y;
+9. }
+</pre>
+</div>
+
+<p>Compiled to LLVM, this function would be represented like this:</p>
+
+<div class="doc_code">
+<pre>
+define void @foo() nounwind ssp {
+entry:
+ %X = alloca i32, align 4 ; &lt;i32*&gt; [#uses=4]
+ %Y = alloca i32, align 4 ; &lt;i32*&gt; [#uses=4]
+ %Z = alloca i32, align 4 ; &lt;i32*&gt; [#uses=3]
+ %0 = bitcast i32* %X to { }* ; &lt;{ }*&gt; [#uses=1]
+ call void @llvm.dbg.declare({ }* %0, metadata !0), !dbg !7
+ store i32 21, i32* %X, !dbg !8
+ %1 = bitcast i32* %Y to { }* ; &lt;{ }*&gt; [#uses=1]
+ call void @llvm.dbg.declare({ }* %1, metadata !9), !dbg !10
+ store i32 22, i32* %Y, !dbg !11
+ %2 = bitcast i32* %Z to { }* ; &lt;{ }*&gt; [#uses=1]
+ call void @llvm.dbg.declare({ }* %2, metadata !12), !dbg !14
+ store i32 23, i32* %Z, !dbg !15
+ %tmp = load i32* %X, !dbg !16 ; &lt;i32&gt; [#uses=1]
+ %tmp1 = load i32* %Y, !dbg !16 ; &lt;i32&gt; [#uses=1]
+ %add = add nsw i32 %tmp, %tmp1, !dbg !16 ; &lt;i32&gt; [#uses=1]
+ store i32 %add, i32* %Z, !dbg !16
+ %tmp2 = load i32* %Y, !dbg !17 ; &lt;i32&gt; [#uses=1]
+ store i32 %tmp2, i32* %X, !dbg !17
+ ret void, !dbg !18
+}
+
+declare void @llvm.dbg.declare({ }*, metadata) nounwind readnone
+
+!0 = metadata !{i32 459008, metadata !1, metadata !"X",
+ metadata !3, i32 2, metadata !6}; [ DW_TAG_auto_variable ]
+!1 = metadata !{i32 458763, metadata !2}; [DW_TAG_lexical_block ]
+!2 = metadata !{i32 458798, i32 0, metadata !3, metadata !"foo", metadata !"foo",
+ metadata !"foo", metadata !3, i32 1, metadata !4,
+ i1 false, i1 true}; [DW_TAG_subprogram ]
+!3 = metadata !{i32 458769, i32 0, i32 12, metadata !"foo.c",
+ metadata !"/private/tmp", metadata !"clang 1.1", i1 true,
+ i1 false, metadata !"", i32 0}; [DW_TAG_compile_unit ]
+!4 = metadata !{i32 458773, metadata !3, metadata !"", null, i32 0, i64 0, i64 0,
+ i64 0, i32 0, null, metadata !5, i32 0}; [DW_TAG_subroutine_type ]
+!5 = metadata !{null}
+!6 = metadata !{i32 458788, metadata !3, metadata !"int", metadata !3, i32 0,
+ i64 32, i64 32, i64 0, i32 0, i32 5}; [DW_TAG_base_type ]
+!7 = metadata !{i32 2, i32 7, metadata !1, null}
+!8 = metadata !{i32 2, i32 3, metadata !1, null}
+!9 = metadata !{i32 459008, metadata !1, metadata !"Y", metadata !3, i32 3,
+ metadata !6}; [ DW_TAG_auto_variable ]
+!10 = metadata !{i32 3, i32 7, metadata !1, null}
+!11 = metadata !{i32 3, i32 3, metadata !1, null}
+!12 = metadata !{i32 459008, metadata !13, metadata !"Z", metadata !3, i32 5,
+ metadata !6}; [ DW_TAG_auto_variable ]
+!13 = metadata !{i32 458763, metadata !1}; [DW_TAG_lexical_block ]
+!14 = metadata !{i32 5, i32 9, metadata !13, null}
+!15 = metadata !{i32 5, i32 5, metadata !13, null}
+!16 = metadata !{i32 6, i32 5, metadata !13, null}
+!17 = metadata !{i32 8, i32 3, metadata !1, null}
+!18 = metadata !{i32 9, i32 1, metadata !2, null}
+</pre>
+</div>
+
+<p>This example illustrates a few important details about LLVM debugging
+ information. In particular, it shows how the <tt>llvm.dbg.declare</tt>
+ intrinsic and location information, which are attached to an instruction,
+ are applied together to allow a debugger to analyze the relationship between
+ statements, variable definitions, and the code used to implement the
+ function.</p>
+
+<div class="doc_code">
+<pre>
+call void @llvm.dbg.declare({ }* %0, metadata !0), !dbg !7
+</pre>
+</div>
+
+<p>The first intrinsic
+ <tt>%<a href="#format_common_declare">llvm.dbg.declare</a></tt>
+ encodes debugging information for the variable <tt>X</tt>. The metadata
+ <tt>!dbg !7</tt> attached to the intrinsic provides scope information for the
+ variable <tt>X</tt>.</p>
+
+<div class="doc_code">
+<pre>
+!7 = metadata !{i32 2, i32 7, metadata !1, null}
+!1 = metadata !{i32 458763, metadata !2}; [DW_TAG_lexical_block ]
+!2 = metadata !{i32 458798, i32 0, metadata !3, metadata !"foo",
+ metadata !"foo", metadata !"foo", metadata !3, i32 1,
+ metadata !4, i1 false, i1 true}; [DW_TAG_subprogram ]
+</pre>
+</div>
+
+<p>Here <tt>!7</tt> is metadata providing location information. It has four
+ fields: line number, column number, scope, and original scope. The original
+ scope represents inline location if this instruction is inlined inside a
+ caller, and is null otherwise. In this example, scope is encoded by
+ <tt>!1</tt>. <tt>!1</tt> represents a lexical block inside the scope
+ <tt>!2</tt>, where <tt>!2</tt> is a
+ <a href="#format_subprograms">subprogram descriptor</a>. This way the
+ location information attached to the intrinsics indicates that the
+ variable <tt>X</tt> is declared at line number 2 at a function level scope in
+ function <tt>foo</tt>.</p>
+
+<p>Now lets take another example.</p>
+
+<div class="doc_code">
+<pre>
+call void @llvm.dbg.declare({ }* %2, metadata !12), !dbg !14
+</pre>
+</div>
+
+<p>The second intrinsic
+ <tt>%<a href="#format_common_declare">llvm.dbg.declare</a></tt>
+ encodes debugging information for variable <tt>Z</tt>. The metadata
+ <tt>!dbg !14</tt> attached to the intrinsic provides scope information for
+ the variable <tt>Z</tt>.</p>
+
+<div class="doc_code">
+<pre>
+!13 = metadata !{i32 458763, metadata !1}; [DW_TAG_lexical_block ]
+!14 = metadata !{i32 5, i32 9, metadata !13, null}
+</pre>
+</div>
+
+<p>Here <tt>!14</tt> indicates that <tt>Z</tt> is declared at line number 5 and
+ column number 9 inside of lexical scope <tt>!13</tt>. The lexical scope
+ itself resides inside of lexical scope <tt>!1</tt> described above.</p>
+
+<p>The scope information attached with each instruction provides a
+ straightforward way to find instructions covered by a scope.</p>
+
+</div>
+
+<!-- *********************************************************************** -->
+<div class="doc_section">
+ <a name="ccxx_frontend">C/C++ front-end specific debug information</a>
+</div>
+<!-- *********************************************************************** -->
+
+<div class="doc_text">
+
+<p>The C and C++ front-ends represent information about the program in a format
+ that is effectively identical
+ to <a href="http://www.eagercon.com/dwarf/dwarf3std.htm">DWARF 3.0</a> in
+ terms of information content. This allows code generators to trivially
+ support native debuggers by generating standard dwarf information, and
+ contains enough information for non-dwarf targets to translate it as
+ needed.</p>
+
+<p>This section describes the forms used to represent C and C++ programs. Other
+ languages could pattern themselves after this (which itself is tuned to
+ representing programs in the same way that DWARF 3 does), or they could
+ choose to provide completely different forms if they don't fit into the DWARF
+ model. As support for debugging information gets added to the various LLVM
+ source-language front-ends, the information used should be documented
+ here.</p>
+
+<p>The following sections provide examples of various C/C++ constructs and the
+ debug information that would best describe those constructs.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="ccxx_compile_units">C/C++ source file information</a>
+</div>
+
+<div class="doc_text">
+
+<p>Given the source files <tt>MySource.cpp</tt> and <tt>MyHeader.h</tt> located
+ in the directory <tt>/Users/mine/sources</tt>, the following code:</p>
+
+<div class="doc_code">
+<pre>
+#include "MyHeader.h"
+
+int main(int argc, char *argv[]) {
+ return 0;
+}
+</pre>
+</div>
+
+<p>a C/C++ front-end would generate the following descriptors:</p>
+
+<div class="doc_code">
+<pre>
+...
+;;
+;; Define the compile unit for the main source file "/Users/mine/sources/MySource.cpp".
+;;
+!2 = metadata !{
+ i32 524305, ;; Tag
+ i32 0, ;; Unused
+ i32 4, ;; Language Id
+ metadata !"MySource.cpp",
+ metadata !"/Users/mine/sources",
+ metadata !"4.2.1 (Based on Apple Inc. build 5649) (LLVM build 00)",
+ i1 true, ;; Main Compile Unit
+ i1 false, ;; Optimized compile unit
+ metadata !"", ;; Compiler flags
+ i32 0} ;; Runtime version
+
+;;
+;; Define the file for the file "/Users/mine/sources/MySource.cpp".
+;;
+!1 = metadata !{
+ i32 524329, ;; Tag
+ metadata !"MySource.cpp",
+ metadata !"/Users/mine/sources",
+ metadata !3 ;; Compile unit
+}
+
+;;
+;; Define the file for the file "/Users/mine/sources/Myheader.h"
+;;
+!3 = metadata !{
+ i32 524329, ;; Tag
+ metadata !"Myheader.h"
+ metadata !"/Users/mine/sources",
+ metadata !3 ;; Compile unit
+}
+
+...
+</pre>
+</div>
+
+<p>llvm::Instruction provides easy access to metadata attached with an
+instruction. One can extract line number information encoded in LLVM IR
+using <tt>Instruction::getMetadata()</tt> and
+<tt>DILocation::getLineNumber()</tt>.
+<pre>
+ if (MDNode *N = I->getMetadata("dbg")) { // Here I is an LLVM instruction
+ DILocation Loc(N); // DILocation is in DebugInfo.h
+ unsigned Line = Loc.getLineNumber();
+ StringRef File = Loc.getFilename();
+ StringRef Dir = Loc.getDirectory();
+ }
+</pre>
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="ccxx_global_variable">C/C++ global variable information</a>
+</div>
+
+<div class="doc_text">
+
+<p>Given an integer global variable declared as follows:</p>
+
+<div class="doc_code">
+<pre>
+int MyGlobal = 100;
+</pre>
+</div>
+
+<p>a C/C++ front-end would generate the following descriptors:</p>
+
+<div class="doc_code">
+<pre>
+;;
+;; Define the global itself.
+;;
+%MyGlobal = global int 100
+...
+;;
+;; List of debug info of globals
+;;
+!llvm.dbg.gv = !{!0}
+
+;;
+;; Define the global variable descriptor. Note the reference to the global
+;; variable anchor and the global variable itself.
+;;
+!0 = metadata !{
+ i32 524340, ;; Tag
+ i32 0, ;; Unused
+ metadata !1, ;; Context
+ metadata !"MyGlobal", ;; Name
+ metadata !"MyGlobal", ;; Display Name
+ metadata !"MyGlobal", ;; Linkage Name
+ metadata !3, ;; Compile Unit
+ i32 1, ;; Line Number
+ metadata !4, ;; Type
+ i1 false, ;; Is a local variable
+ i1 true, ;; Is this a definition
+ i32* @MyGlobal ;; The global variable
+}
+
+;;
+;; Define the basic type of 32 bit signed integer. Note that since int is an
+;; intrinsic type the source file is NULL and line 0.
+;;
+!4 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"int", ;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 32, ;; Size in Bits
+ i64 32, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 5 ;; Encoding
+}
+
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="ccxx_subprogram">C/C++ function information</a>
+</div>
+
+<div class="doc_text">
+
+<p>Given a function declared as follows:</p>
+
+<div class="doc_code">
+<pre>
+int main(int argc, char *argv[]) {
+ return 0;
+}
+</pre>
+</div>
+
+<p>a C/C++ front-end would generate the following descriptors:</p>
+
+<div class="doc_code">
+<pre>
+;;
+;; Define the anchor for subprograms. Note that the second field of the
+;; anchor is 46, which is the same as the tag for subprograms
+;; (46 = DW_TAG_subprogram.)
+;;
+!6 = metadata !{
+ i32 524334, ;; Tag
+ i32 0, ;; Unused
+ metadata !1, ;; Context
+ metadata !"main", ;; Name
+ metadata !"main", ;; Display name
+ metadata !"main", ;; Linkage name
+ metadata !1, ;; File
+ i32 1, ;; Line number
+ metadata !4, ;; Type
+ i1 false, ;; Is local
+ i1 true ;; Is definition
+}
+;;
+;; Define the subprogram itself.
+;;
+define i32 @main(i32 %argc, i8** %argv) {
+...
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="ccxx_basic_types">C/C++ basic types</a>
+</div>
+
+<div class="doc_text">
+
+<p>The following are the basic type descriptors for C/C++ core types:</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="ccxx_basic_type_bool">bool</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"bool", ;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 8, ;; Size in Bits
+ i64 8, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 2 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="ccxx_basic_char">char</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"char", ;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 8, ;; Size in Bits
+ i64 8, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 6 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="ccxx_basic_unsigned_char">unsigned char</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"unsigned char",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 8, ;; Size in Bits
+ i64 8, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 8 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="ccxx_basic_short">short</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"short int",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 16, ;; Size in Bits
+ i64 16, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 5 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="ccxx_basic_unsigned_short">unsigned short</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"short unsigned int",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 16, ;; Size in Bits
+ i64 16, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 7 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="ccxx_basic_int">int</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"int", ;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 32, ;; Size in Bits
+ i64 32, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 5 ;; Encoding
+}
+</pre></div>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="ccxx_basic_unsigned_int">unsigned int</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"unsigned int",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 32, ;; Size in Bits
+ i64 32, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 7 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="ccxx_basic_long_long">long long</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"long long int",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 64, ;; Size in Bits
+ i64 64, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 5 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="ccxx_basic_unsigned_long_long">unsigned long long</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"long long unsigned int",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 64, ;; Size in Bits
+ i64 64, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 7 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="ccxx_basic_float">float</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"float",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 32, ;; Size in Bits
+ i64 32, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 4 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsubsection">
+ <a name="ccxx_basic_double">double</a>
+</div>
+
+<div class="doc_text">
+
+<div class="doc_code">
+<pre>
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"double",;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 64, ;; Size in Bits
+ i64 64, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 4 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="ccxx_derived_types">C/C++ derived types</a>
+</div>
+
+<div class="doc_text">
+
+<p>Given the following as an example of C/C++ derived type:</p>
+
+<div class="doc_code">
+<pre>
+typedef const int *IntPtr;
+</pre>
+</div>
+
+<p>a C/C++ front-end would generate the following descriptors:</p>
+
+<div class="doc_code">
+<pre>
+;;
+;; Define the typedef "IntPtr".
+;;
+!2 = metadata !{
+ i32 524310, ;; Tag
+ metadata !1, ;; Context
+ metadata !"IntPtr", ;; Name
+ metadata !3, ;; File
+ i32 0, ;; Line number
+ i64 0, ;; Size in bits
+ i64 0, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ metadata !4 ;; Derived From type
+}
+
+;;
+;; Define the pointer type.
+;;
+!4 = metadata !{
+ i32 524303, ;; Tag
+ metadata !1, ;; Context
+ metadata !"", ;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 64, ;; Size in bits
+ i64 64, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ metadata !5 ;; Derived From type
+}
+;;
+;; Define the const type.
+;;
+!5 = metadata !{
+ i32 524326, ;; Tag
+ metadata !1, ;; Context
+ metadata !"", ;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 32, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ metadata !6 ;; Derived From type
+}
+;;
+;; Define the int type.
+;;
+!6 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"int", ;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 32, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ 5 ;; Encoding
+}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="ccxx_composite_types">C/C++ struct/union types</a>
+</div>
+
+<div class="doc_text">
+
+<p>Given the following as an example of C/C++ struct type:</p>
+
+<div class="doc_code">
+<pre>
+struct Color {
+ unsigned Red;
+ unsigned Green;
+ unsigned Blue;
+};
+</pre>
+</div>
+
+<p>a C/C++ front-end would generate the following descriptors:</p>
+
+<div class="doc_code">
+<pre>
+;;
+;; Define basic type for unsigned int.
+;;
+!5 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"unsigned int",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 32, ;; Size in Bits
+ i64 32, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 7 ;; Encoding
+}
+;;
+;; Define composite type for struct Color.
+;;
+!2 = metadata !{
+ i32 524307, ;; Tag
+ metadata !1, ;; Context
+ metadata !"Color", ;; Name
+ metadata !1, ;; Compile unit
+ i32 1, ;; Line number
+ i64 96, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ null, ;; Derived From
+ metadata !3, ;; Elements
+ i32 0 ;; Runtime Language
+}
+
+;;
+;; Define the Red field.
+;;
+!4 = metadata !{
+ i32 524301, ;; Tag
+ metadata !1, ;; Context
+ metadata !"Red", ;; Name
+ metadata !1, ;; File
+ i32 2, ;; Line number
+ i64 32, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ metadata !5 ;; Derived From type
+}
+
+;;
+;; Define the Green field.
+;;
+!6 = metadata !{
+ i32 524301, ;; Tag
+ metadata !1, ;; Context
+ metadata !"Green", ;; Name
+ metadata !1, ;; File
+ i32 3, ;; Line number
+ i64 32, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 32, ;; Offset in bits
+ i32 0, ;; Flags
+ metadata !5 ;; Derived From type
+}
+
+;;
+;; Define the Blue field.
+;;
+!7 = metadata !{
+ i32 524301, ;; Tag
+ metadata !1, ;; Context
+ metadata !"Blue", ;; Name
+ metadata !1, ;; File
+ i32 4, ;; Line number
+ i64 32, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 64, ;; Offset in bits
+ i32 0, ;; Flags
+ metadata !5 ;; Derived From type
+}
+
+;;
+;; Define the array of fields used by the composite type Color.
+;;
+!3 = metadata !{metadata !4, metadata !6, metadata !7}
+</pre>
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="ccxx_enumeration_types">C/C++ enumeration types</a>
+</div>
+
+<div class="doc_text">
+
+<p>Given the following as an example of C/C++ enumeration type:</p>
+
+<div class="doc_code">
+<pre>
+enum Trees {
+ Spruce = 100,
+ Oak = 200,
+ Maple = 300
+};
+</pre>
+</div>
+
+<p>a C/C++ front-end would generate the following descriptors:</p>
+
+<div class="doc_code">
+<pre>
+;;
+;; Define composite type for enum Trees
+;;
+!2 = metadata !{
+ i32 524292, ;; Tag
+ metadata !1, ;; Context
+ metadata !"Trees", ;; Name
+ metadata !1, ;; File
+ i32 1, ;; Line number
+ i64 32, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ null, ;; Derived From type
+ metadata !3, ;; Elements
+ i32 0 ;; Runtime language
+}
+
+;;
+;; Define the array of enumerators used by composite type Trees.
+;;
+!3 = metadata !{metadata !4, metadata !5, metadata !6}
+
+;;
+;; Define Spruce enumerator.
+;;
+!4 = metadata !{i32 524328, metadata !"Spruce", i64 100}
+
+;;
+;; Define Oak enumerator.
+;;
+!5 = metadata !{i32 524328, metadata !"Oak", i64 200}
+
+;;
+;; Define Maple enumerator.
+;;
+!6 = metadata !{i32 524328, metadata !"Maple", i64 300}
+
+</pre>
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+
+<hr>
+<address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
+
+ <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
+ <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date$
+</address>
+
+</body>
+</html>
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