Reviewers: danno,
Message:
MSan bug is fixed in LLVM trunk. This change would let us make progress
without
waiting for LLVM roll in Chromium.
Description:
MSan workaround in Simulator::VisitBitfield.
This change shuffles the code in Simulator::VisitBitfield a bit
to work around a MemorySanitizer bug. New code should not be any
slower or less readable than before.
More info:
https://code.google.com/p/memory-sanitizer/issues/detail?id=50
Please review this at https://codereview.chromium.org/212863002/
SVN Base: http://v8.googlecode.com/svn/branches/bleeding_edge/
Affected files (+3, -2 lines):
M src/arm64/simulator-arm64.cc
Index: src/arm64/simulator-arm64.cc
===================================================================
--- src/arm64/simulator-arm64.cc (revision 20276)
+++ src/arm64/simulator-arm64.cc (working copy)
@@ -2108,8 +2108,9 @@
// Rotate source bitfield into place.
int64_t result = (static_cast<uint64_t>(src) >> R) | (src << (reg_size -
R));
// Determine the sign extension.
- int64_t topbits = ((1L << (reg_size - diff - 1)) - 1) << (diff + 1);
- int64_t signbits = extend && ((src >> S) & 1) ? topbits : 0;
+ int64_t topbits_preshift = (1L << (reg_size - diff - 1)) - 1;
+ int64_t signbits = (extend && ((src >> S) & 1) ? topbits_preshift : 0)
+ << (diff + 1);
// Merge sign extension, dest/zero and bitfield.
result = signbits | (result & mask) | (dst & ~mask);
--
--
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