[llvm-branch-commits] [llvm-branch] r86925 - in /llvm/branches/Apple/Leela: lib/CodeGen/BranchFolding.cpp lib/CodeGen/BranchFolding.h test/CodeGen/X86/tail-opts.ll
Dan Gohman
gohman at apple.com
Wed Nov 11 17:43:39 PST 2009
Author: djg
Date: Wed Nov 11 19:43:39 2009
New Revision: 86925
URL: http://llvm.org/viewvc/llvm-project?rev=86925&view=rev
Log:
$ svn merge -c 86885 https://djg@llvm.org/svn/llvm-project/llvm/trunk
--- Merging r86885 into '.':
U lib/CodeGen/BranchFolding.cpp
U lib/CodeGen/BranchFolding.h
$ svn merge -c 86909 https://djg@llvm.org/svn/llvm-project/llvm/trunk
--- Merging r86909 into '.':
U test/CodeGen/X86/tail-opts.ll
G lib/CodeGen/BranchFolding.cpp
Modified:
llvm/branches/Apple/Leela/lib/CodeGen/BranchFolding.cpp
llvm/branches/Apple/Leela/lib/CodeGen/BranchFolding.h
llvm/branches/Apple/Leela/test/CodeGen/X86/tail-opts.ll
Modified: llvm/branches/Apple/Leela/lib/CodeGen/BranchFolding.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/branches/Apple/Leela/lib/CodeGen/BranchFolding.cpp?rev=86925&r1=86924&r2=86925&view=diff
==============================================================================
--- llvm/branches/Apple/Leela/lib/CodeGen/BranchFolding.cpp (original)
+++ llvm/branches/Apple/Leela/lib/CodeGen/BranchFolding.cpp Wed Nov 11 19:43:39 2009
@@ -429,24 +429,24 @@
TII->InsertBranch(*CurMBB, SuccBB, NULL, SmallVector<MachineOperand, 0>());
}
-static bool MergeCompare(const std::pair<unsigned,MachineBasicBlock*> &p,
- const std::pair<unsigned,MachineBasicBlock*> &q) {
- if (p.first < q.first)
- return true;
- else if (p.first > q.first)
- return false;
- else if (p.second->getNumber() < q.second->getNumber())
- return true;
- else if (p.second->getNumber() > q.second->getNumber())
- return false;
- else {
- // _GLIBCXX_DEBUG checks strict weak ordering, which involves comparing
- // an object with itself.
+bool
+BranchFolder::MergePotentialsElt::operator<(const MergePotentialsElt &o) const {
+ if (getHash() < o.getHash())
+ return true;
+ else if (getHash() > o.getHash())
+ return false;
+ else if (getBlock()->getNumber() < o.getBlock()->getNumber())
+ return true;
+ else if (getBlock()->getNumber() > o.getBlock()->getNumber())
+ return false;
+ else {
+ // _GLIBCXX_DEBUG checks strict weak ordering, which involves comparing
+ // an object with itself.
#ifndef _GLIBCXX_DEBUG
- llvm_unreachable("Predecessor appears twice");
+ llvm_unreachable("Predecessor appears twice");
#endif
- return false;
- }
+ return false;
+ }
}
/// CountTerminators - Count the number of terminators in the given
@@ -495,6 +495,15 @@
return true;
}
+ // If one of the blocks can be completely merged and happens to be in
+ // a position where the other could fall through into it, merge any number
+ // of instructions, because it can be done without a branch.
+ // TODO: If the blocks are not adjacent, move one of them so that they are?
+ if (MBB1->isLayoutSuccessor(MBB2) && I2 == MBB2->begin())
+ return true;
+ if (MBB2->isLayoutSuccessor(MBB1) && I1 == MBB1->begin())
+ return true;
+
// If both blocks have an unconditional branch temporarily stripped out,
// treat that as an additional common instruction.
if (MBB1 != PredBB && MBB2 != PredBB &&
@@ -537,22 +546,23 @@
MPIterator HighestMPIter = prior(MergePotentials.end());
for (MPIterator CurMPIter = prior(MergePotentials.end()),
B = MergePotentials.begin();
- CurMPIter!=B && CurMPIter->first == CurHash;
+ CurMPIter!=B && CurMPIter->getHash() == CurHash;
--CurMPIter) {
- for (MPIterator I = prior(CurMPIter); I->first == CurHash ; --I) {
+ for (MPIterator I = prior(CurMPIter); I->getHash() == CurHash ; --I) {
unsigned CommonTailLen;
- if (ProfitableToMerge(CurMPIter->second, I->second, minCommonTailLength,
+ if (ProfitableToMerge(CurMPIter->getBlock(), I->getBlock(),
+ minCommonTailLength,
CommonTailLen, TrialBBI1, TrialBBI2,
SuccBB, PredBB)) {
if (CommonTailLen > maxCommonTailLength) {
SameTails.clear();
maxCommonTailLength = CommonTailLen;
HighestMPIter = CurMPIter;
- SameTails.push_back(std::make_pair(CurMPIter, TrialBBI1));
+ SameTails.push_back(SameTailElt(CurMPIter, TrialBBI1));
}
if (HighestMPIter == CurMPIter &&
CommonTailLen == maxCommonTailLength)
- SameTails.push_back(std::make_pair(I, TrialBBI2));
+ SameTails.push_back(SameTailElt(I, TrialBBI2));
}
if (I == B)
break;
@@ -568,16 +578,16 @@
MachineBasicBlock* PredBB) {
MPIterator CurMPIter, B;
for (CurMPIter = prior(MergePotentials.end()), B = MergePotentials.begin();
- CurMPIter->first == CurHash;
+ CurMPIter->getHash() == CurHash;
--CurMPIter) {
// Put the unconditional branch back, if we need one.
- MachineBasicBlock *CurMBB = CurMPIter->second;
+ MachineBasicBlock *CurMBB = CurMPIter->getBlock();
if (SuccBB && CurMBB != PredBB)
FixTail(CurMBB, SuccBB, TII);
if (CurMPIter == B)
break;
}
- if (CurMPIter->first!=CurHash)
+ if (CurMPIter->getHash() != CurHash)
CurMPIter++;
MergePotentials.erase(CurMPIter, MergePotentials.end());
}
@@ -590,29 +600,30 @@
unsigned TimeEstimate = ~0U;
for (i=0, commonTailIndex=0; i<SameTails.size(); i++) {
// Use PredBB if possible; that doesn't require a new branch.
- if (SameTails[i].first->second == PredBB) {
+ if (SameTails[i].getBlock() == PredBB) {
commonTailIndex = i;
break;
}
// Otherwise, make a (fairly bogus) choice based on estimate of
// how long it will take the various blocks to execute.
- unsigned t = EstimateRuntime(SameTails[i].first->second->begin(),
- SameTails[i].second);
+ unsigned t = EstimateRuntime(SameTails[i].getBlock()->begin(),
+ SameTails[i].getTailStartPos());
if (t <= TimeEstimate) {
TimeEstimate = t;
commonTailIndex = i;
}
}
- MachineBasicBlock::iterator BBI = SameTails[commonTailIndex].second;
- MachineBasicBlock *MBB = SameTails[commonTailIndex].first->second;
+ MachineBasicBlock::iterator BBI =
+ SameTails[commonTailIndex].getTailStartPos();
+ MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock();
DEBUG(errs() << "\nSplitting BB#" << MBB->getNumber() << ", size "
<< maxCommonTailLength);
MachineBasicBlock *newMBB = SplitMBBAt(*MBB, BBI);
- SameTails[commonTailIndex].first->second = newMBB;
- SameTails[commonTailIndex].second = newMBB->begin();
+ SameTails[commonTailIndex].setBlock(newMBB);
+ SameTails[commonTailIndex].setTailStartPos(newMBB->begin());
// If we split PredBB, newMBB is the new predecessor.
if (PredBB == MBB)
@@ -641,22 +652,22 @@
// new branching and as such are very likely to be profitable.
if (SuccBB) {
if (SuccBB->pred_size() == MergePotentials.size() &&
- !MergePotentials[0].second->empty()) {
+ !MergePotentials[0].getBlock()->empty()) {
// If all the predecessors have at least one tail instruction in common,
// merging is very likely to be a win since it won't require an increase
// in static branches, and it will decrease the static instruction count.
bool AllPredsMatch = true;
MachineBasicBlock::iterator FirstNonTerm;
- unsigned MinNumTerms = CountTerminators(MergePotentials[0].second,
+ unsigned MinNumTerms = CountTerminators(MergePotentials[0].getBlock(),
FirstNonTerm);
- if (FirstNonTerm != MergePotentials[0].second->end()) {
+ if (FirstNonTerm != MergePotentials[0].getBlock()->end()) {
for (unsigned i = 1, e = MergePotentials.size(); i != e; ++i) {
MachineBasicBlock::iterator OtherFirstNonTerm;
- unsigned NumTerms = CountTerminators(MergePotentials[0].second,
+ unsigned NumTerms = CountTerminators(MergePotentials[0].getBlock(),
OtherFirstNonTerm);
if (NumTerms < MinNumTerms)
MinNumTerms = NumTerms;
- if (OtherFirstNonTerm == MergePotentials[i].second->end() ||
+ if (OtherFirstNonTerm == MergePotentials[i].getBlock()->end() ||
OtherFirstNonTerm->isIdenticalTo(FirstNonTerm)) {
AllPredsMatch = false;
break;
@@ -672,7 +683,7 @@
DEBUG(errs() << "\nTryTailMergeBlocks: ";
for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i)
- errs() << "BB#" << MergePotentials[i].second->getNumber()
+ errs() << "BB#" << MergePotentials[i].getBlock()->getNumber()
<< (i == e-1 ? "" : ", ");
errs() << "\n";
if (SuccBB) {
@@ -688,11 +699,11 @@
// Sort by hash value so that blocks with identical end sequences sort
// together.
- std::stable_sort(MergePotentials.begin(), MergePotentials.end(),MergeCompare);
+ std::stable_sort(MergePotentials.begin(), MergePotentials.end());
// Walk through equivalence sets looking for actual exact matches.
while (MergePotentials.size() > 1) {
- unsigned CurHash = MergePotentials.back().first;
+ unsigned CurHash = MergePotentials.back().getHash();
// Build SameTails, identifying the set of blocks with this hash code
// and with the maximum number of instructions in common.
@@ -711,31 +722,45 @@
// block, which we can't jump to), we can treat all blocks with this same
// tail at once. Use PredBB if that is one of the possibilities, as that
// will not introduce any extra branches.
- MachineBasicBlock *EntryBB = MergePotentials.begin()->second->
- getParent()->begin();
- unsigned int commonTailIndex, i;
- for (commonTailIndex=SameTails.size(), i=0; i<SameTails.size(); i++) {
- MachineBasicBlock *MBB = SameTails[i].first->second;
- if (MBB == EntryBB)
- continue;
- if (MBB == PredBB) {
- commonTailIndex = i;
- break;
+ MachineBasicBlock *EntryBB = MergePotentials.begin()->getBlock()->
+ getParent()->begin();
+ unsigned commonTailIndex = SameTails.size();
+ // If there are two blocks, check to see if one can be made to fall through
+ // into the other.
+ if (SameTails.size() == 2 &&
+ SameTails[0].getBlock()->isLayoutSuccessor(SameTails[1].getBlock()) &&
+ SameTails[1].tailIsWholeBlock())
+ commonTailIndex = 1;
+ else if (SameTails.size() == 2 &&
+ SameTails[1].getBlock()->isLayoutSuccessor(
+ SameTails[0].getBlock()) &&
+ SameTails[0].tailIsWholeBlock())
+ commonTailIndex = 0;
+ else {
+ // Otherwise just pick one, favoring the fall-through predecessor if
+ // there is one.
+ for (unsigned i = 0, e = SameTails.size(); i != e; ++i) {
+ MachineBasicBlock *MBB = SameTails[i].getBlock();
+ if (MBB == EntryBB && SameTails[i].tailIsWholeBlock())
+ continue;
+ if (MBB == PredBB) {
+ commonTailIndex = i;
+ break;
+ }
+ if (SameTails[i].tailIsWholeBlock())
+ commonTailIndex = i;
}
- if (MBB->begin() == SameTails[i].second)
- commonTailIndex = i;
}
if (commonTailIndex == SameTails.size() ||
- (SameTails[commonTailIndex].first->second == PredBB &&
- SameTails[commonTailIndex].first->second->begin() !=
- SameTails[i].second)) {
+ (SameTails[commonTailIndex].getBlock() == PredBB &&
+ !SameTails[commonTailIndex].tailIsWholeBlock())) {
// None of the blocks consist entirely of the common tail.
// Split a block so that one does.
commonTailIndex = CreateCommonTailOnlyBlock(PredBB, maxCommonTailLength);
}
- MachineBasicBlock *MBB = SameTails[commonTailIndex].first->second;
+ MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock();
// MBB is common tail. Adjust all other BB's to jump to this one.
// Traversal must be forwards so erases work.
DEBUG(errs() << "\nUsing common tail in BB#" << MBB->getNumber()
@@ -743,12 +768,12 @@
for (unsigned int i=0, e = SameTails.size(); i != e; ++i) {
if (commonTailIndex == i)
continue;
- DEBUG(errs() << "BB#" << SameTails[i].first->second->getNumber()
+ DEBUG(errs() << "BB#" << SameTails[i].getBlock()->getNumber()
<< (i == e-1 ? "" : ", "));
// Hack the end off BB i, making it jump to BB commonTailIndex instead.
- ReplaceTailWithBranchTo(SameTails[i].second, MBB);
+ ReplaceTailWithBranchTo(SameTails[i].getTailStartPos(), MBB);
// BB i is no longer a predecessor of SuccBB; remove it from the worklist.
- MergePotentials.erase(SameTails[i].first);
+ MergePotentials.erase(SameTails[i].getMPIter());
}
DEBUG(errs() << "\n");
// We leave commonTailIndex in the worklist in case there are other blocks
@@ -768,7 +793,7 @@
MergePotentials.clear();
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
if (I->succ_empty())
- MergePotentials.push_back(std::make_pair(HashEndOfMBB(I, 2U), I));
+ MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(I, 2U), I));
}
// See if we can do any tail merging on those.
@@ -854,7 +879,8 @@
// reinsert conditional branch only, for now
TII->InsertBranch(*PBB, (TBB == IBB) ? FBB : TBB, 0, NewCond);
}
- MergePotentials.push_back(std::make_pair(HashEndOfMBB(PBB, 1U), *P));
+ MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(PBB, 1U),
+ *P));
}
}
if (MergePotentials.size() >= 2)
@@ -863,8 +889,8 @@
// The 1 below can occur as a result of removing blocks in TryTailMergeBlocks.
PredBB = prior(I); // this may have been changed in TryTailMergeBlocks
if (MergePotentials.size() == 1 &&
- MergePotentials.begin()->second != PredBB)
- FixTail(MergePotentials.begin()->second, IBB, TII);
+ MergePotentials.begin()->getBlock() != PredBB)
+ FixTail(MergePotentials.begin()->getBlock(), IBB, TII);
}
}
return MadeChange;
@@ -1047,7 +1073,7 @@
continue;
// Don't duplicate into a fall-through predecessor unless its the
// only predecessor.
- if (&*next(MachineFunction::iterator(PredBB)) == TailBB &&
+ if (PredBB->isLayoutSuccessor(TailBB) &&
PrevFallsThrough &&
TailBB->pred_size() != 1)
continue;
Modified: llvm/branches/Apple/Leela/lib/CodeGen/BranchFolding.h
URL: http://llvm.org/viewvc/llvm-project/llvm/branches/Apple/Leela/lib/CodeGen/BranchFolding.h?rev=86925&r1=86924&r2=86925&view=diff
==============================================================================
--- llvm/branches/Apple/Leela/lib/CodeGen/BranchFolding.h (original)
+++ llvm/branches/Apple/Leela/lib/CodeGen/BranchFolding.h Wed Nov 11 19:43:39 2009
@@ -30,11 +30,58 @@
const TargetRegisterInfo *tri,
MachineModuleInfo *mmi);
private:
- typedef std::pair<unsigned,MachineBasicBlock*> MergePotentialsElt;
+ class MergePotentialsElt {
+ unsigned Hash;
+ MachineBasicBlock *Block;
+ public:
+ MergePotentialsElt(unsigned h, MachineBasicBlock *b)
+ : Hash(h), Block(b) {}
+
+ unsigned getHash() const { return Hash; }
+ MachineBasicBlock *getBlock() const { return Block; }
+
+ void setBlock(MachineBasicBlock *MBB) {
+ Block = MBB;
+ }
+
+ bool operator<(const MergePotentialsElt &) const;
+ };
typedef std::vector<MergePotentialsElt>::iterator MPIterator;
std::vector<MergePotentialsElt> MergePotentials;
- typedef std::pair<MPIterator, MachineBasicBlock::iterator> SameTailElt;
+ class SameTailElt {
+ MPIterator MPIter;
+ MachineBasicBlock::iterator TailStartPos;
+ public:
+ SameTailElt(MPIterator mp, MachineBasicBlock::iterator tsp)
+ : MPIter(mp), TailStartPos(tsp) {}
+
+ MPIterator getMPIter() const {
+ return MPIter;
+ }
+ MergePotentialsElt &getMergePotentialsElt() const {
+ return *getMPIter();
+ }
+ MachineBasicBlock::iterator getTailStartPos() const {
+ return TailStartPos;
+ }
+ unsigned getHash() const {
+ return getMergePotentialsElt().getHash();
+ }
+ MachineBasicBlock *getBlock() const {
+ return getMergePotentialsElt().getBlock();
+ }
+ bool tailIsWholeBlock() const {
+ return TailStartPos == getBlock()->begin();
+ }
+
+ void setBlock(MachineBasicBlock *MBB) {
+ getMergePotentialsElt().setBlock(MBB);
+ }
+ void setTailStartPos(MachineBasicBlock::iterator Pos) {
+ TailStartPos = Pos;
+ }
+ };
std::vector<SameTailElt> SameTails;
bool EnableTailMerge;
Modified: llvm/branches/Apple/Leela/test/CodeGen/X86/tail-opts.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/branches/Apple/Leela/test/CodeGen/X86/tail-opts.ll?rev=86925&r1=86924&r2=86925&view=diff
==============================================================================
--- llvm/branches/Apple/Leela/test/CodeGen/X86/tail-opts.ll (original)
+++ llvm/branches/Apple/Leela/test/CodeGen/X86/tail-opts.ll Wed Nov 11 19:43:39 2009
@@ -266,3 +266,30 @@
declare fastcc i32 @lvalue_p(%union.tree_node* nocapture) nounwind readonly
declare fastcc %union.tree_node* @default_conversion(%union.tree_node*) nounwind
+
+
+; If one tail merging candidate falls through into the other,
+; tail merging is likely profitable regardless of how few
+; instructions are involved. This function should have only
+; one ret instruction.
+
+; CHECK: foo:
+; CHECK: call func
+; CHECK-NEXT: .LBB5_2:
+; CHECK-NEXT: addq $8, %rsp
+; CHECK-NEXT: ret
+
+define void @foo(i1* %V) nounwind {
+entry:
+ %t0 = icmp eq i1* %V, null
+ br i1 %t0, label %return, label %bb
+
+bb:
+ call void @func()
+ ret void
+
+return:
+ ret void
+}
+
+declare void @func()
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