Add a new attribute called 'jumptable' that creates jump-instruction tables for functions marked with this attribute.

It includes a pass that rewrites all indirect calls to jumptable functions to pass through these tables.

This also adds backend support for generating the jump-instruction tables on ARM and X86.
Note that since the jumptable attribute creates a second function pointer for a
function, any function marked with jumptable must also be marked with unnamed_addr.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210280 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 8 insertions, 0 deletions

diff --git a/docs/LangRef.rst b/docs/LangRef.rst
index d76fc0d3af..6beb9652ed 100644
--- a/docs/LangRef.rst
+++ b/docs/LangRef.rst
@@ -1020,6 +1020,14 @@ example:
     inlining this function is desirable (such as the "inline" keyword in
     C/C++). It is just a hint; it imposes no requirements on the
     inliner.
+``jumptable``
+    This attribute indicates that the function should be added to a
+    jump-instruction table at code-generation time, and that all address-taken
+    references to this function should be replaced with a reference to the
+    appropriate jump-instruction-table function pointer. Note that this creates
+    a new pointer for the original function, which means that code that depends
+    on function-pointer identity can break. So, any function annotated with
+    ``jumptable`` must also be ``unnamed_addr``.
 ``minsize``
     This attribute suggests that optimization passes and code generator
     passes make choices that keep the code size of this function as small