Add a comment mentioning that InstructionSimplify routines do,

in fact, resolve undef uses.

llvm-svn: 173721

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/include/llvm/Analysis/InstructionSimplify.h b/llvm/include/llvm/Analysis/InstructionSimplify.h
index b653e799f7c..06e44329676 100644
--- a/llvm/include/llvm/Analysis/InstructionSimplify.h
+++ b/llvm/include/llvm/Analysis/InstructionSimplify.h
@@ -14,6 +14,12 @@
 // ("and i32 %x, %x" -> "%x").  If the simplification is also an instruction
 // then it dominates the original instruction.
 //
+// These routines implicitly resolve undef uses. The easiest way to be safe when
+// using these routines to obtain simplified values for existing instructions is
+// to always replace all uses of the instructions with the resulting simplified
+// values. This will prevent other code from seeing the same undef uses and
+// resolving them to different values.
+//
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_ANALYSIS_INSTRUCTIONSIMPLIFY_H