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Make isAliased property for fixed-offset stack objects adjustable

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We used to assume that any fixed-offset stack object was not aliased. This
meant that no IR value could point to the memory contained in such an object.
This is a reasonable default, but is not a universally-correct
target-independent fact. For example, on PowerPC (both Darwin and non-Darwin),
some byval arguments are allocated at fixed offsets by the ABI. These, however,
certainly can be pointed to by IR values. This change moves the 'isAliased'
logic out of FixedStackPseudoSourceValue and into MFI, and allows the isAliased
property to be overridden for fixed-offset objects.

This will be used by an upcoming commit to the PowerPC backend to fix PR20280.

No functionality change intended (the behavior of
FixedStackPseudoSourceValue::isAliased has been made more conservative for
callers that don't pass an MFI object, but I don't see any in-tree callers that
do that).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215794 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hal Finkel
2014-08-16 00:17:02 +00:00
parent bdd8b6bfb9
commit 227df4bca0
3 changed files with 29 additions and 16 deletions
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8
lib/CodeGen/PseudoSourceValue.cpp
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@@ -107,13 +107,9 @@ bool FixedStackPseudoSourceValue::isConstant(const MachineFrameInfo *MFI) const{
}
bool FixedStackPseudoSourceValue::isAliased(const MachineFrameInfo *MFI) const {
// Negative frame indices are used for special things that don't
// appear in LLVM IR. Non-negative indices may be used for things
// like static allocas.
if (!MFI)
return FI >= 0;
// Spill slots should not alias others.
return !MFI->isFixedObjectIndex(FI) && !MFI->isSpillSlotObjectIndex(FI);
return true;
return MFI->isAliasedObjectIndex(FI);
}
bool FixedStackPseudoSourceValue::mayAlias(const MachineFrameInfo *MFI) const {