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Merge in fix for PR9561.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_29@128354 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bill Wendling 2011-03-27 00:42:33 +00:00
parent 59460aba2e
commit db2629e109
1 changed files with 23 additions and 14 deletions
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37
lib/Transforms/Scalar/DeadStoreElimination.cpp
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@ -340,24 +340,33 @@ static bool isCompleteOverwrite(const AliasAnalysis::Location &Later,
// Okay, we have stores to two completely different pointers. Try to
// decompose the pointer into a "base + constant_offset" form. If the base
// pointers are equal, then we can reason about the two stores.
int64_t Off1 = 0, Off2 = 0;
const Value *BP1 = GetPointerBaseWithConstantOffset(P1, Off1, TD);
const Value *BP2 = GetPointerBaseWithConstantOffset(P2, Off2, TD);
int64_t EarlierOff = 0, LaterOff = 0;
const Value *BP1 = GetPointerBaseWithConstantOffset(P1, EarlierOff, TD);
const Value *BP2 = GetPointerBaseWithConstantOffset(P2, LaterOff, TD);
// If the base pointers still differ, we have two completely different stores.
if (BP1 != BP2)
return false;
// Otherwise, we might have a situation like:
// store i16 -> P + 1 Byte
// store i32 -> P
// In this case, we see if the later store completely overlaps all bytes
// stored by the previous store.
if (Off1 < Off2 || // Earlier starts before Later.
Off1+Earlier.Size > Off2+Later.Size) // Earlier goes beyond Later.
return false;
// Otherwise, we have complete overlap.
return true;
// The later store completely overlaps the earlier store if:
//
// 1. Both start at the same offset and the later one's size is greater than
// or equal to the earlier one's, or
//
// |--earlier--|
// |-- later --|
//
// 2. The earlier store has an offset greater than the later offset, but which
// still lies completely within the later store.
//
// |--earlier--|
// |----- later ------|
if (EarlierOff >= LaterOff &&
EarlierOff + Earlier.Size <= LaterOff + Later.Size)
return true;
// Otherwise, they don't completely overlap.
return false;
}
/// isPossibleSelfRead - If 'Inst' might be a self read (i.e. a noop copy of a