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https://github.com/c64scene-ar/llvm-6502.git
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Skeleton for transformations to truncate loop's iteration space.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@42054 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Devang Patel
parent
8c33da5dc4
commit
5279d064bc
@ -111,7 +111,14 @@ namespace {
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/// instruction then loop body is executed only for one iteration. In
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/// such case eliminate loop structure surrounding this loop body. For
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bool processOneIterationLoop(SplitInfo &SD);
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void updateLoopBounds(ICmpInst *CI);
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/// updateLoopIterationSpace - Current loop body is covered by an AND
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/// instruction whose operands compares induction variables with loop
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/// invariants. If possible, hoist this check outside the loop by
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/// updating appropriate start and end values for induction variable.
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bool updateLoopIterationSpace(SplitInfo &SD);
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/// If loop header includes loop variant instruction operands then
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/// this loop may not be eliminated.
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bool safeHeader(SplitInfo &SD, BasicBlock *BB);
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@ -229,7 +236,19 @@ bool LoopIndexSplit::runOnLoop(Loop *IncomingLoop, LPPassManager &LPM_Ref) {
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E = SplitData.end(); SI != E;) {
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SplitInfo &SD = *SI;
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ICmpInst *CI = dyn_cast<ICmpInst>(SD.SplitCondition);
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if (CI && CI->getPredicate() == ICmpInst::ICMP_EQ) {
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if (SD.SplitCondition->getOpcode() == Instruction::And) {
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Changed = updateLoopIterationSpace(SD);
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if (Changed) {
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++NumIndexSplit;
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// If is loop is eliminated then nothing else to do here.
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return Changed;
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} else {
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SmallVector<SplitInfo, 4>::iterator Delete_SI = SI;
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++SI;
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SplitData.erase(Delete_SI);
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}
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}
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else if (CI && CI->getPredicate() == ICmpInst::ICMP_EQ) {
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Changed = processOneIterationLoop(SD);
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if (Changed) {
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++NumIndexSplit;
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@ -391,6 +410,25 @@ void LoopIndexSplit::findSplitCondition() {
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if (BR->isUnconditional())
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continue;
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if (Instruction *AndI = dyn_cast<Instruction>(BR->getCondition())) {
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if (AndI->getOpcode() == Instruction::And) {
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ICmpInst *Op0 = dyn_cast<ICmpInst>(AndI->getOperand(0));
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ICmpInst *Op1 = dyn_cast<ICmpInst>(AndI->getOperand(1));
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if (!Op0 || !Op1)
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continue;
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if (!safeICmpInst(Op0, SD))
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continue;
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SD.clear();
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if (!safeICmpInst(Op1, SD))
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continue;
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SD.clear();
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SD.SplitCondition = AndI;
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SplitData.push_back(SD);
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continue;
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}
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}
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ICmpInst *CI = dyn_cast<ICmpInst>(BR->getCondition());
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if (!CI || CI == ExitCondition)
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continue;
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@ -662,6 +700,164 @@ bool LoopIndexSplit::safeExitingBlock(SplitInfo &SD,
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return true;
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}
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void LoopIndexSplit::updateLoopBounds(ICmpInst *CI) {
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Value *V0 = CI->getOperand(0);
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Value *V1 = CI->getOperand(1);
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Value *NV = NULL;
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SCEVHandle SH0 = SE->getSCEV(V0);
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if (SH0->isLoopInvariant(L))
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NV = V0;
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else
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NV = V1;
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switch (CI->getPredicate()) {
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case ICmpInst::ICMP_ULE:
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case ICmpInst::ICMP_SLE:
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// for (i = LB; i < UB; ++i)
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// if (i <= NV && ...)
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// LOOP_BODY
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//
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// is transformed into
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// NUB = min (NV+1, UB)
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// for (i = LB; i < NUB ; ++i)
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// LOOP_BODY
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//
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// for (i = LB; i <= UB; ++i)
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// if (i <= NV && ...)
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// LOOP_BODY
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//
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// is transformed into
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// NUB = min (NV, UB)
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// for (i = LB; i <= NUB ; ++i)
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// LOOP_BODY
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//
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break;
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case ICmpInst::ICMP_ULT:
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case ICmpInst::ICMP_SLT:
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// for (i = LB; i < UB; ++i)
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// if (i < NV && ...)
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// LOOP_BODY
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//
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// is transformed into
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// NUB = min (NV, UB)
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// for (i = LB; i < NUB ; ++i)
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// LOOP_BODY
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//
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// for (i = LB; i <= UB; ++i)
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// if (i < NV && ...)
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// LOOP_BODY
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//
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// is transformed into
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// NUB = min (NV -1 , UB)
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// for (i = LB; i <= NUB ; ++i)
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// LOOP_BODY
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//
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break;
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case ICmpInst::ICMP_UGE:
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case ICmpInst::ICMP_SGE:
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// for (i = LB; i (< or <=) UB; ++i)
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// if (i >= NV && ...)
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// LOOP_BODY
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//
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// is transformed into
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// NLB = max (NV, LB)
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// for (i = NLB; i (< or <=) UB ; ++i)
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// LOOP_BODY
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//
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break;
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case ICmpInst::ICMP_UGT:
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case ICmpInst::ICMP_SGT:
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// for (i = LB; i (< or <=) UB; ++i)
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// if (i > NV && ...)
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// LOOP_BODY
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//
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// is transformed into
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// NLB = max (NV+1, LB)
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// for (i = NLB; i (< or <=) UB ; ++i)
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// LOOP_BODY
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//
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break;
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default:
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assert ( 0 && "Unexpected split condition predicate");
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}
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}
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/// updateLoopIterationSpace - Current loop body is covered by an AND
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/// instruction whose operands compares induction variables with loop
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/// invariants. If possible, hoist this check outside the loop by
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/// updating appropriate start and end values for induction variable.
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bool LoopIndexSplit::updateLoopIterationSpace(SplitInfo &SD) {
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BasicBlock *Header = L->getHeader();
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ICmpInst *Op0 = cast<ICmpInst>(SD.SplitCondition->getOperand(0));
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ICmpInst *Op1 = cast<ICmpInst>(SD.SplitCondition->getOperand(1));
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if (Op0->getPredicate() == ICmpInst::ICMP_EQ
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|| Op0->getPredicate() == ICmpInst::ICMP_NE
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|| Op0->getPredicate() == ICmpInst::ICMP_EQ
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|| Op0->getPredicate() == ICmpInst::ICMP_NE)
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return false;
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// Check if SplitCondition dominates entire loop body
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// or not.
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// If SplitCondition is not in loop header then this loop is not suitable
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// for this transformation.
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if (SD.SplitCondition->getParent() != Header)
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return false;
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// If loop header includes loop variant instruction operands then
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// this loop may not be eliminated.
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Instruction *Terminator = Header->getTerminator();
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for(BasicBlock::iterator BI = Header->begin(), BE = Header->end();
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BI != BE; ++BI) {
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Instruction *I = BI;
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// PHI Nodes are OK.
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if (isa<PHINode>(I))
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continue;
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// SplitCondition itself is OK.
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if (I == SD.SplitCondition)
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continue;
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if (I == Op0 || I == Op1)
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continue;
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// Induction variable is OK.
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if (I == IndVar)
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continue;
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// Induction variable increment is OK.
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if (I == IndVarIncrement)
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continue;
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// Terminator is also harmless.
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if (I == Terminator)
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continue;
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// Otherwise we have a instruction that may not be safe.
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return false;
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}
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// If Exiting block includes loop variant instructions then this
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// loop may not be eliminated.
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if (!safeExitingBlock(SD, ExitCondition->getParent()))
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return false;
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updateLoopBounds(Op0);
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updateLoopBounds(Op1);
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// Update CFG
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return true;
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}
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/// removeBlocks - Remove basic block DeadBB and all blocks dominated by DeadBB.
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/// This routine is used to remove split condition's dead branch, dominated by
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/// DeadBB. LiveBB dominates split conidition's other branch.
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