[ifcnv] Add comment explaining why it's OK to duplicate convergent MIs in ifcnv.
Summary:
Also add a comment briefly explaining what ifcnv is.
No functional changes.
Reviewers: resistor
Subscribers: echristo, tra, llvm-commits
Differential Revision: http://reviews.llvm.org/D17430
llvm-svn: 261543
diff --git a/llvm/lib/CodeGen/IfConversion.cpp b/llvm/lib/CodeGen/IfConversion.cpp
index 41f9f0b..a8e72f4 100644
--- a/llvm/lib/CodeGen/IfConversion.cpp
+++ b/llvm/lib/CodeGen/IfConversion.cpp
@@ -7,7 +7,8 @@
//
//===----------------------------------------------------------------------===//
//
-// This file implements the machine instruction level if-conversion pass.
+// This file implements the machine instruction level if-conversion pass, which
+// tries to convert conditional branches into predicated instructions.
//
//===----------------------------------------------------------------------===//
@@ -673,6 +674,9 @@
if (I->isDebugValue())
continue;
+ // Don't need to check isConvergent(). It's OK to duplicate convergent
+ // instructions here, because we'll only push convergent operations up the
+ // CFG -- this can only *remove* control-flow dependencies.
if (I->isNotDuplicable())
BBI.CannotBeCopied = true;