PNaCl ABI: Strip out arithmetic attributes "nsw", "nuw" and "exact"

"nsw" and "nuw" -- "no signed wrap" and "no unsigned wrap" -- are not
used by the backend, which is not surprising because it makes no
difference to the hardware if arithmetic overflows.

Although "exact" is used by the backend to convert "sdiv exact" to an
"ashr" shift, it appears that "sdiv exact" does not get used in
practice, and arguably such a transformation belongs in the user
toolchain, not the PNaCl translator.

BUG=https://code.google.com/p/nativeclient/issues/detail?id=3483
TEST=*.ll tests + PNaCl toolchain trybots

Review URL: https://codereview.chromium.org/16746005

1 files changed, 8 insertions, 0 deletions

diff --git a/lib/Transforms/NaCl/StripAttributes.cpp b/lib/Transforms/NaCl/StripAttributes.cpp
index 476c500756..8074353472 100644
--- a/lib/Transforms/NaCl/StripAttributes.cpp
+++ b/lib/Transforms/NaCl/StripAttributes.cpp
@@ -22,6 +22,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/IR/Function.h"
+#include "llvm/IR/Operator.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/CallSite.h"
 #include "llvm/Transforms/NaCl.h"
@@ -144,6 +145,13 @@ bool StripAttributes::runOnFunction(Function &Func) {
         CheckAttributes(Call.getAttributes());
         Call.setAttributes(AttributeSet());
         Call.setCallingConv(CallingConv::C);
+      } else if (OverflowingBinaryOperator *Op =
+                     dyn_cast<OverflowingBinaryOperator>(Inst)) {
+        cast<BinaryOperator>(Op)->setHasNoUnsignedWrap(false);
+        cast<BinaryOperator>(Op)->setHasNoSignedWrap(false);
+      } else if (PossiblyExactOperator *Op =
+                     dyn_cast<PossiblyExactOperator>(Inst)) {
+        cast<BinaryOperator>(Op)->setIsExact(false);
       }
     }
   }