Use a memcpy so that type based alias analysis sees the change.

The other option would be to do something like

if (that.isSingleWord())
  VAL = that.VAL;
else
  pVal = that.pVal

This bug was causing 86TTI::getIntImmCost to be miscompiled in a LTO
bootstrap in stage2, causing the build of stage3 to fail.

LLVM is getting quiet good at exploiting this. Not sure if there is anything
a sanitizer could do to help

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222294 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/ADT/APInt.h b/include/llvm/ADT/APInt.h
index 4d19bab13f43b1f66547830b07f19caa6392b359..f4e7e3c635656677c9dcd7465445f635d0d090d6 100644 (file)
--- a/include/llvm/ADT/APInt.h
+++ b/include/llvm/ADT/APInt.h
@@ -665,7 +665,9 @@ public:
       delete[] pVal;
     }
 
-    VAL = that.VAL;
+    // Use memcpy so that type based alias analysis sees both VAL and pVal
+    // as modified.
+    memcpy(&VAL, &that.VAL, sizeof(uint64_t));
 
     // If 'this == &that', avoid zeroing our own bitwidth by storing to 'that'
     // first.