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[BranchFolding] Merge MMOs during tail merge

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Summary:
If we remove the MMOs from Load/Store instructions,
they are treated as volatile. This makes other optimization passes unhappy.
eg. Load/Store Optimization

So, it looks better to merge, not remove.

Reviewers: gberry, mcrosier

Subscribers: gberry, llvm-commits

Differential Revision: http://reviews.llvm.org/D14797



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@254694 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Junmo Park 2015-12-04 02:29:25 +00:00
parent 51540fbf42
commit 64649a7dc7
1 changed files with 26 additions and 16 deletions
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42
lib/CodeGen/BranchFolding.cpp
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@ -744,24 +744,35 @@ bool BranchFolder::CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB,
return true;
}
static bool hasIdenticalMMOs(const MachineInstr *MI1, const MachineInstr *MI2) {
// Add MI1's MMOs to MI2's MMOs while excluding any duplicates. The MI scheduler
// currently doesn't handle multiple MMOs, so duplicates would likely pessimize
// the scheduler.
static void mergeMMOs(MachineInstr *MI1, MachineInstr *MI2) {
auto I1 = MI1->memoperands_begin(), E1 = MI1->memoperands_end();
auto I2 = MI2->memoperands_begin(), E2 = MI2->memoperands_end();
if ((E1 - I1) != (E2 - I2))
return false;
for (; I1 != E1; ++I1, ++I2) {
if (**I1 != **I2)
return false;
MachineFunction *MF = MI1->getParent()->getParent();
// Mostly, MI1's MMO count is 1 or zero. So we don't have to use
// SmallSet.
for (; I1 != E1; ++I1) {
bool IsDupMMO = false;
for (I2 = MI2->memoperands_begin(); I2 != E2; ++I2) {
if (**I1 == **I2) {
IsDupMMO = true;
break;
}
}
if (IsDupMMO == false) {
MI2->addMemOperand(*MF, *I1);
E2 = MI2->memoperands_end();
}
}
return true;
}
static void
removeMMOsFromMemoryOperations(MachineBasicBlock::iterator MBBIStartPos,
MachineBasicBlock &MBBCommon) {
// Remove MMOs from memory operations in the common block
// when they do not match the ones from the block being tail-merged.
// This ensures later passes conservatively compute dependencies.
mergeMMOsFromMemoryOperations(MachineBasicBlock::iterator MBBIStartPos,
MachineBasicBlock &MBBCommon) {
// Merge MMOs from memory operations in the common block
MachineBasicBlock *MBB = MBBIStartPos->getParent();
// Note CommonTailLen does not necessarily matches the size of
// the common BB nor all its instructions because of debug
@ -792,8 +803,7 @@ removeMMOsFromMemoryOperations(MachineBasicBlock::iterator MBBIStartPos,
assert(MBBICommon->isIdenticalTo(&*MBBI) && "Expected matching MIIs!");
if (MBBICommon->mayLoad() || MBBICommon->mayStore())
if (!hasIdenticalMMOs(&*MBBI, &*MBBICommon))
MBBICommon->clearMemRefs();
mergeMMOs(&*MBBI, &*MBBICommon);
++MBBI;
++MBBICommon;
@ -913,8 +923,8 @@ bool BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB,
continue;
DEBUG(dbgs() << "BB#" << SameTails[i].getBlock()->getNumber()
<< (i == e-1 ? "" : ", "));
// Remove MMOs from memory operations as needed.
removeMMOsFromMemoryOperations(SameTails[i].getTailStartPos(), *MBB);
// Merge MMOs from memory operations as needed.
mergeMMOsFromMemoryOperations(SameTails[i].getTailStartPos(), *MBB);
// Hack the end off BB i, making it jump to BB commonTailIndex instead.
ReplaceTailWithBranchTo(SameTails[i].getTailStartPos(), MBB);
// BB i is no longer a predecessor of SuccBB; remove it from the worklist.