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Generalize OptimizeLoopTermCond to optimize more loop terminating icmp to use postinc iv.
llvm-svn: 89116
This commit is contained in:
Evan Cheng
parent
801e8e8291
commit
aaa58b7653
@ -2414,7 +2414,7 @@ bool LoopStrengthReduce::StrideMightBeShared(const SCEV* Stride, Loop *L,
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/// conditional branch or it's and / or with other conditions before being used
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/// as the condition.
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static bool isUsedByExitBranch(ICmpInst *Cond, Loop *L) {
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BasicBlock *CondBB = Cond->getParent();
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BasicBlock *CondBB = Cond->getParent();
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if (!L->isLoopExiting(CondBB))
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return false;
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BranchInst *TermBr = dyn_cast<BranchInst>(CondBB->getTerminator());
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@ -2482,106 +2482,119 @@ static bool ShouldCountToZero(ICmpInst *Cond, IVStrideUse* &CondUse,
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/// OptimizeLoopTermCond - Change loop terminating condition to use the
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/// postinc iv when possible.
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void LoopStrengthReduce::OptimizeLoopTermCond(Loop *L) {
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// Finally, get the terminating condition for the loop if possible. If we
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// can, we want to change it to use a post-incremented version of its
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// induction variable, to allow coalescing the live ranges for the IV into
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// one register value.
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BasicBlock *LatchBlock = L->getLoopLatch();
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BasicBlock *ExitingBlock = L->getExitingBlock();
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bool LatchExit = L->isLoopExiting(LatchBlock);
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SmallVector<BasicBlock*, 8> ExitingBlocks;
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L->getExitingBlocks(ExitingBlocks);
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if (!ExitingBlock)
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// Multiple exits, just look at the exit in the latch block if there is one.
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ExitingBlock = LatchBlock;
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BranchInst *TermBr = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
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if (!TermBr)
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return;
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if (TermBr->isUnconditional() || !isa<ICmpInst>(TermBr->getCondition()))
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return;
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for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
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BasicBlock *ExitingBlock = ExitingBlocks[i];
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// Search IVUsesByStride to find Cond's IVUse if there is one.
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IVStrideUse *CondUse = 0;
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const SCEV *CondStride = 0;
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ICmpInst *Cond = cast<ICmpInst>(TermBr->getCondition());
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if (!FindIVUserForCond(Cond, CondUse, CondStride))
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return;
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// Finally, get the terminating condition for the loop if possible. If we
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// can, we want to change it to use a post-incremented version of its
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// induction variable, to allow coalescing the live ranges for the IV into
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// one register value.
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bool UsePostInc = true;
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if (ExitingBlock != LatchBlock) {
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if (Cond->hasOneUse()) {
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// See below, we don't want the condition to be cloned.
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BranchInst *TermBr = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
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if (!TermBr)
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continue;
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// FIXME: Overly conservative, termination condition could be an 'or' etc..
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if (TermBr->isUnconditional() || !isa<ICmpInst>(TermBr->getCondition()))
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continue;
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// If exiting block is the latch block, we know it's safe and profitable
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// to transform the icmp to use post-inc iv. Otherwise do so only if it
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// would not reuse another iv and its iv would be reused by other uses.
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// We are optimizing for the case where the icmp is the only use of the
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// iv.
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IVUsersOfOneStride &StrideUses = *IU->IVUsesByStride[CondStride];
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for (ilist<IVStrideUse>::iterator I = StrideUses.Users.begin(),
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E = StrideUses.Users.end(); I != E; ++I) {
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if (I->getUser() == Cond)
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continue;
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if (!I->isUseOfPostIncrementedValue()) {
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UsePostInc = false;
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break;
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// Search IVUsesByStride to find Cond's IVUse if there is one.
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IVStrideUse *CondUse = 0;
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const SCEV *CondStride = 0;
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ICmpInst *Cond = cast<ICmpInst>(TermBr->getCondition());
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if (!FindIVUserForCond(Cond, CondUse, CondStride))
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continue;
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// If the latch block is exiting and it's not a single block loop, it's
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// not safe to use postinc iv in other exiting blocks. FIXME: overly
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// conservative? How about icmp stride optimization?
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bool UsePostInc = !(e > 1 && LatchExit && ExitingBlock != LatchBlock);
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if (UsePostInc && ExitingBlock != LatchBlock) {
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if (!Cond->hasOneUse())
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// See below, we don't want the condition to be cloned.
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UsePostInc = false;
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else {
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// If exiting block is the latch block, we know it's safe and profitable
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// to transform the icmp to use post-inc iv. Otherwise do so only if it
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// would not reuse another iv and its iv would be reused by other uses.
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// We are optimizing for the case where the icmp is the only use of the
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// iv.
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IVUsersOfOneStride &StrideUses = *IU->IVUsesByStride[CondStride];
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for (ilist<IVStrideUse>::iterator I = StrideUses.Users.begin(),
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E = StrideUses.Users.end(); I != E; ++I) {
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if (I->getUser() == Cond)
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continue;
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if (!I->isUseOfPostIncrementedValue()) {
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UsePostInc = false;
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break;
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}
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}
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}
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// If iv for the stride might be shared and any of the users use pre-inc
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// iv might be used, then it's not safe to use post-inc iv.
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if (UsePostInc &&
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isa<SCEVConstant>(CondStride) &&
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StrideMightBeShared(CondStride, L, true))
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UsePostInc = false;
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}
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// If the trip count is computed in terms of a max (due to ScalarEvolution
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// being unable to find a sufficient guard, for example), change the loop
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// comparison to use SLT or ULT instead of NE.
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Cond = OptimizeMax(L, Cond, CondUse);
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// If possible, change stride and operands of the compare instruction to
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// eliminate one stride. However, avoid rewriting the compare instruction
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// with an iv of new stride if it's likely the new stride uses will be
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// rewritten using the stride of the compare instruction.
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if (ExitingBlock == LatchBlock && isa<SCEVConstant>(CondStride)) {
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// If the condition stride is a constant and it's the only use, we might
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// want to optimize it first by turning it to count toward zero.
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if (!StrideMightBeShared(CondStride, L, false) &&
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!ShouldCountToZero(Cond, CondUse, SE, L, TLI))
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Cond = ChangeCompareStride(L, Cond, CondUse, CondStride);
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}
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if (!UsePostInc)
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continue;
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DEBUG(errs() << " Change loop exiting icmp to use postinc iv: "
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<< *Cond << '\n');
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// It's possible for the setcc instruction to be anywhere in the loop, and
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// possible for it to have multiple users. If it is not immediately before
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// the exiting block branch, move it.
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if (&*++BasicBlock::iterator(Cond) != (Instruction*)TermBr) {
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if (Cond->hasOneUse()) { // Condition has a single use, just move it.
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Cond->moveBefore(TermBr);
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} else {
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// Otherwise, clone the terminating condition and insert into the
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// loopend.
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Cond = cast<ICmpInst>(Cond->clone());
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Cond->setName(L->getHeader()->getName() + ".termcond");
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ExitingBlock->getInstList().insert(TermBr, Cond);
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// Clone the IVUse, as the old use still exists!
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IU->IVUsesByStride[CondStride]->addUser(CondUse->getOffset(), Cond,
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CondUse->getOperandValToReplace());
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CondUse = &IU->IVUsesByStride[CondStride]->Users.back();
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}
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}
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// If iv for the stride might be shared and any of the users use pre-inc iv
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// might be used, then it's not safe to use post-inc iv.
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if (UsePostInc &&
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isa<SCEVConstant>(CondStride) &&
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StrideMightBeShared(CondStride, L, true))
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UsePostInc = false;
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// If we get to here, we know that we can transform the setcc instruction to
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// use the post-incremented version of the IV, allowing us to coalesce the
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// live ranges for the IV correctly.
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CondUse->setOffset(SE->getMinusSCEV(CondUse->getOffset(), CondStride));
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CondUse->setIsUseOfPostIncrementedValue(true);
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Changed = true;
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++NumLoopCond;
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}
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// If the trip count is computed in terms of a max (due to ScalarEvolution
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// being unable to find a sufficient guard, for example), change the loop
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// comparison to use SLT or ULT instead of NE.
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Cond = OptimizeMax(L, Cond, CondUse);
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// If possible, change stride and operands of the compare instruction to
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// eliminate one stride. However, avoid rewriting the compare instruction with
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// an iv of new stride if it's likely the new stride uses will be rewritten
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// using the stride of the compare instruction.
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if (ExitingBlock == LatchBlock && isa<SCEVConstant>(CondStride)) {
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// If the condition stride is a constant and it's the only use, we might
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// want to optimize it first by turning it to count toward zero.
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if (!StrideMightBeShared(CondStride, L, false) &&
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!ShouldCountToZero(Cond, CondUse, SE, L, TLI))
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Cond = ChangeCompareStride(L, Cond, CondUse, CondStride);
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}
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if (!UsePostInc)
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return;
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// It's possible for the setcc instruction to be anywhere in the loop, and
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// possible for it to have multiple users. If it is not immediately before
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// the latch block branch, move it.
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if (&*++BasicBlock::iterator(Cond) != (Instruction*)TermBr) {
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if (Cond->hasOneUse()) { // Condition has a single use, just move it.
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Cond->moveBefore(TermBr);
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} else {
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// Otherwise, clone the terminating condition and insert into the loopend.
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Cond = cast<ICmpInst>(Cond->clone());
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Cond->setName(L->getHeader()->getName() + ".termcond");
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LatchBlock->getInstList().insert(TermBr, Cond);
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// Clone the IVUse, as the old use still exists!
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IU->IVUsesByStride[CondStride]->addUser(CondUse->getOffset(), Cond,
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CondUse->getOperandValToReplace());
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CondUse = &IU->IVUsesByStride[CondStride]->Users.back();
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}
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}
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// If we get to here, we know that we can transform the setcc instruction to
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// use the post-incremented version of the IV, allowing us to coalesce the
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// live ranges for the IV correctly.
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CondUse->setOffset(SE->getMinusSCEV(CondUse->getOffset(), CondStride));
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CondUse->setIsUseOfPostIncrementedValue(true);
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Changed = true;
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++NumLoopCond;
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}
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bool LoopStrengthReduce::OptimizeLoopCountIVOfStride(const SCEV* &Stride,
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@ -2728,7 +2741,6 @@ bool LoopStrengthReduce::OptimizeLoopCountIV(Loop *L) {
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}
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bool LoopStrengthReduce::runOnLoop(Loop *L, LPPassManager &LPM) {
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IU = &getAnalysis<IVUsers>();
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LI = &getAnalysis<LoopInfo>();
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DT = &getAnalysis<DominatorTree>();
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27
test/Transforms/LoopStrengthReduce/icmp_use_postinc.ll
Normal file
27
test/Transforms/LoopStrengthReduce/icmp_use_postinc.ll
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@ -0,0 +1,27 @@
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; RUN: opt < %s -loop-reduce -S | FileCheck %s
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define i32 @main(i32 %argc, i8** nocapture %argv) nounwind ssp {
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entry:
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br i1 undef, label %bb4.preheader, label %bb.nph8
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bb4.preheader: ; preds = %entry
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br label %bb4
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bb1: ; preds = %bb4
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br i1 undef, label %bb.nph8, label %bb3
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bb3: ; preds = %bb1
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%phitmp = add i32 %indvar, 1 ; <i32> [#uses=1]
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br label %bb4
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bb4: ; preds = %bb3, %bb4.preheader
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; CHECK: %lsr.iv = phi
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; CHECK: %lsr.iv.next = add i32 %lsr.iv, 1
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; CHECK: %0 = icmp slt i32 %lsr.iv.next, %argc
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%indvar = phi i32 [ 1, %bb4.preheader ], [ %phitmp, %bb3 ] ; <i32> [#uses=2]
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%0 = icmp slt i32 %indvar, %argc ; <i1> [#uses=1]
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br i1 %0, label %bb1, label %bb.nph8
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bb.nph8: ; preds = %bb4, %bb1, %entry
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unreachable
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}
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