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[ARM] Align stack objects passed to memory intrinsics

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Memcpy, and other memory intrinsics, typically tries to use LDM/STM if
the source and target addresses are 4-byte aligned. In CodeGenPrepare
look for calls to memory intrinsics and, if the object is on the
stack, 4-byte align it if it's large enough that we expect that memcpy
would want to use LDM/STM to copy it.

Differential Revision: http://reviews.llvm.org/D7908


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232627 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
John Brawn
2015-03-18 12:01:59 +00:00
parent bf60cd0751
commit 0328ca6cd7
6 changed files with 337 additions and 21 deletions
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lib/CodeGen/CodeGenPrepare.cpp
+36
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@@ -1228,6 +1228,42 @@ bool CodeGenPrepare::OptimizeCallInst(CallInst *CI, bool& ModifiedDT) {
return true;
}
const DataLayout *TD = TLI ? TLI->getDataLayout() : nullptr;
// Align the pointer arguments to this call if the target thinks it's a good
// idea
unsigned MinSize, PrefAlign;
if (TLI && TD && TLI->shouldAlignPointerArgs(CI, MinSize, PrefAlign)) {
for (auto &Arg : CI->arg_operands()) {
// We want to align both objects whose address is used directly and
// objects whose address is used in casts and GEPs, though it only makes
// sense for GEPs if the offset is a multiple of the desired alignment and
// if size - offset meets the size threshold.
if (!Arg->getType()->isPointerTy())
continue;
APInt Offset(TD->getPointerSizeInBits(
cast<PointerType>(Arg->getType())->getAddressSpace()), 0);
Value *Val = Arg->stripAndAccumulateInBoundsConstantOffsets(*TD, Offset);
uint64_t Offset2 = Offset.getLimitedValue();
AllocaInst *AI;
if ((Offset2 & (PrefAlign-1)) == 0 &&
(AI = dyn_cast<AllocaInst>(Val)) &&
AI->getAlignment() < PrefAlign &&
TD->getTypeAllocSize(AI->getAllocatedType()) >= MinSize + Offset2)
AI->setAlignment(PrefAlign);
// TODO: Also align GlobalVariables
}
// If this is a memcpy (or similar) then we may be able to improve the
// alignment
if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(CI)) {
unsigned Align = getKnownAlignment(MI->getDest(), *TD);
if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI))
Align = std::min(Align, getKnownAlignment(MTI->getSource(), *TD));
if (Align > MI->getAlignment())
MI->setAlignment(ConstantInt::get(MI->getAlignmentType(), Align));
}
}
IntrinsicInst *II = dyn_cast<IntrinsicInst>(CI);
if (II) {
switch (II->getIntrinsicID()) {