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scudo: Simplify getClassIdBySize() logic. NFCI. 

By subtracting 1 from Size at the beginning we can simplify the
subsequent calculations. This also saves 4 instructions on aarch64
and 9 instructions on x86_64, but seems to be perf neutral.

Differential Revision: https://reviews.llvm.org/D73936
This commit is contained in:
Peter Collingbourne 2020-02-03 15:35:35 -08:00
parent 9271cab270
commit f7de7084f4
1 changed files with 4 additions and 4 deletions
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8
compiler-rt/lib/scudo/standalone/size_class_map.h
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@ -66,11 +66,11 @@ public:
DCHECK_LE(Size, MaxSize);
if (Size <= MidSize)
return (Size + MinSize - 1) >> MinSizeLog;
Size -= 1;
const uptr L = getMostSignificantSetBitIndex(Size);
const uptr HBits = (Size >> (L - S)) & M;
const uptr LBits = Size & ((1UL << (L - S)) - 1);
const uptr L1 = L - MidSizeLog;
return MidClass + (L1 << S) + HBits + (LBits > 0);
const uptr LBits = (Size >> (L - S)) - (1 << S);
const uptr HBits = (L - MidSizeLog) << S;
return MidClass + 1 + HBits + LBits;
}
static u32 getMaxCachedHint(uptr Size) {