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Diffstat (limited to 'docs/LangRef.html')
| -rw-r--r-- | docs/LangRef.html | 38 |
1 files changed, 35 insertions, 3 deletions
diff --git a/docs/LangRef.html b/docs/LangRef.html index 1b94ab5a9a..8c52a2118e 100644 --- a/docs/LangRef.html +++ b/docs/LangRef.html @@ -89,6 +89,7 @@ <li><a href="#complexconstants">Complex Constants</a></li> <li><a href="#globalconstants">Global Variable and Function Addresses</a></li> <li><a href="#undefvalues">Undefined Values</a></li> + <li><a href="#trapvalues">Trap Values</a></li> <li><a href="#blockaddress">Addresses of Basic Blocks</a></li> <li><a href="#constantexprs">Constant Expressions</a></li> </ol> @@ -2303,6 +2304,34 @@ has undefined behavior.</p> </div> <!-- ======================================================================= --> +<div class="doc_subsection"><a name="trapvalues">Trap Values</a></div> +<div class="doc_text"> + +<p>Trap values are similar to <a href="undefvalues">undef values</a>, however + instead of representing an unspecified bit pattern, they represent the + fact that an instruction or constant expression which cannot evoke side + effects has nevertheless detected a condition which results in undefined + behavior.<p> + +<p>Any non-void instruction or constant expression other than non-intrinsic + calls or invokes with a trap operand has trap as its result value. + Any instruction with a trap operand which may have side effects emits + those side effects as if it had an undef operand instead.</p> + +<p>For example, an <a href="#i_and"><tt>and</tt></a> of a trap value with + zero still has a trap value result. Using that value as an index in a + <a href="#i_getelementptr"><tt>getelementptr</tt></a> yields a trap + result. Using that result as the address of a + <a href="#i_store"><tt>store</tt></a> produces undefined behavior.</p> + +<p>There is currently no way of representing a trap constant in the IR; they + only exist when produced by certain instructions, such as an + <a href="#i_add"><tt>add</tt></a> with the <tt>nsw</tt> flag + set, when overflow occurs.</p> + +</div> + +<!-- ======================================================================= --> <div class="doc_subsection"><a name="blockaddress">Addresses of Basic Blocks</a></div> <div class="doc_text"> @@ -3104,7 +3133,8 @@ Instruction</a> </div> <p><tt>nuw</tt> and <tt>nsw</tt> stand for "No Unsigned Wrap" and "No Signed Wrap", respectively. If the <tt>nuw</tt> and/or <tt>nsw</tt> keywords are present, the result value of the <tt>add</tt> - is undefined if unsigned and/or signed overflow, respectively, occurs.</p> + is a <a href="#trapvalues">trap value</a> if unsigned and/or signed overflow, + respectively, occurs.</p> <h5>Example:</h5> <pre> @@ -3184,7 +3214,8 @@ Instruction</a> </div> <p><tt>nuw</tt> and <tt>nsw</tt> stand for "No Unsigned Wrap" and "No Signed Wrap", respectively. If the <tt>nuw</tt> and/or <tt>nsw</tt> keywords are present, the result value of the <tt>sub</tt> - is undefined if unsigned and/or signed overflow, respectively, occurs.</p> + is a <a href="#trapvalues">trap value</a> if unsigned and/or signed overflow, + respectively, occurs.</p> <h5>Example:</h5> <pre> @@ -3270,7 +3301,8 @@ Instruction</a> </div> <p><tt>nuw</tt> and <tt>nsw</tt> stand for "No Unsigned Wrap" and "No Signed Wrap", respectively. If the <tt>nuw</tt> and/or <tt>nsw</tt> keywords are present, the result value of the <tt>mul</tt> - is undefined if unsigned and/or signed overflow, respectively, occurs.</p> + is a <a href="#trapvalues">trap value</a> if unsigned and/or signed overflow, + respectively, occurs.</p> <h5>Example:</h5> <pre> |