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Fix the LoopUnroller to handle nontrivial loops and partial unrolling.
These are not individual bug fixes. I had to rewrite a good chunk of the unroller to make it sane. I think it was getting lucky on trivial completely unrolled loops with no early exits. I included some fairly simple unit tests for partial unrolling. I didn't do much stress testing, so it may not be perfect, but should be usable now. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@137190 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrew Trick
parent
33e57515b1
commit
b1eede1281
@ -134,6 +134,11 @@ public:
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block_iterator block_begin() const { return Blocks.begin(); }
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block_iterator block_end() const { return Blocks.end(); }
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/// getNumBlocks - Get the number of blocks in this loop.
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unsigned getNumBlocks() const {
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return std::distance(block_begin(), block_end());
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}
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/// isLoopExiting - True if terminator in the block can branch to another
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/// block that is outside of the current loop.
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///
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@ -21,6 +21,7 @@
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#include "llvm/BasicBlock.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/LoopIterator.h"
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#include "llvm/Analysis/LoopPass.h"
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#include "llvm/Analysis/ScalarEvolution.h"
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#include "llvm/Support/Debug.h"
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@ -225,11 +226,25 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
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Headers.push_back(Header);
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Latches.push_back(LatchBlock);
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// The current on-the-fly SSA update requires blocks to be processed in
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// reverse postorder so that LastValueMap contains the correct value at each
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// exit.
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LoopBlocksDFS DFS(L);
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{
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// Traverse the loop blocks using depth-first search to record RPO numbers
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// for each block in the DFS result.
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LoopBlocksTraversal Traversal(DFS, LI);
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for (LoopBlocksTraversal::POTIterator POI = Traversal.begin(),
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POE = Traversal.end(); POI != POE; ++POI);
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}
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// Stash the DFS iterators before adding blocks to the loop.
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LoopBlocksDFS::RPOIterator BlockBegin = DFS.beginRPO();
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LoopBlocksDFS::RPOIterator BlockEnd = DFS.endRPO();
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for (unsigned It = 1; It != Count; ++It) {
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std::vector<BasicBlock*> NewBlocks;
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for (std::vector<BasicBlock*>::iterator BB = LoopBlocks.begin(),
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E = LoopBlocks.end(); BB != E; ++BB) {
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for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) {
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ValueToValueMapTy VMap;
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BasicBlock *New = CloneBasicBlock(*BB, VMap, "." + Twine(It));
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Header->getParent()->getBasicBlockList().push_back(New);
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@ -255,35 +270,27 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
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L->addBasicBlockToLoop(New, LI->getBase());
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// Add phi entries for newly created values to all exit blocks except
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// the successor of the latch block. The successor of the exit block will
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// be updated specially after unrolling all the way.
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if (*BB != LatchBlock)
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for (succ_iterator SI = succ_begin(*BB), SE = succ_end(*BB); SI != SE;
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++SI)
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if (!L->contains(*SI))
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for (BasicBlock::iterator BBI = (*SI)->begin();
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PHINode *phi = dyn_cast<PHINode>(BBI); ++BBI) {
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Value *Incoming = phi->getIncomingValueForBlock(*BB);
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phi->addIncoming(Incoming, New);
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}
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// Add phi entries for newly created values to all exit blocks.
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for (succ_iterator SI = succ_begin(*BB), SE = succ_end(*BB);
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SI != SE; ++SI) {
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if (L->contains(*SI))
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continue;
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for (BasicBlock::iterator BBI = (*SI)->begin();
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PHINode *phi = dyn_cast<PHINode>(BBI); ++BBI) {
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Value *Incoming = phi->getIncomingValueForBlock(*BB);
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ValueToValueMapTy::iterator It = LastValueMap.find(Incoming);
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if (It != LastValueMap.end())
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Incoming = It->second;
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phi->addIncoming(Incoming, New);
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}
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}
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// Keep track of new headers and latches as we create them, so that
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// we can insert the proper branches later.
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if (*BB == Header)
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Headers.push_back(New);
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if (*BB == LatchBlock) {
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if (*BB == LatchBlock)
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Latches.push_back(New);
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// Also, clear out the new latch's back edge so that it doesn't look
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// like a new loop, so that it's amenable to being merged with adjacent
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// blocks later on.
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TerminatorInst *Term = New->getTerminator();
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assert(L->contains(Term->getSuccessor(!ContinueOnTrue)));
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assert(Term->getSuccessor(ContinueOnTrue) == LoopExit);
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Term->setSuccessor(!ContinueOnTrue, NULL);
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}
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NewBlocks.push_back(New);
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}
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@ -294,36 +301,24 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
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::RemapInstruction(I, LastValueMap);
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}
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// The latch block exits the loop. If there are any PHI nodes in the
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// successor blocks, update them to use the appropriate values computed as the
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// last iteration of the loop.
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if (Count != 1) {
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BasicBlock *LastIterationBB = cast<BasicBlock>(LastValueMap[LatchBlock]);
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for (succ_iterator SI = succ_begin(LatchBlock), SE = succ_end(LatchBlock);
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SI != SE; ++SI) {
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for (BasicBlock::iterator BBI = (*SI)->begin();
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PHINode *PN = dyn_cast<PHINode>(BBI); ++BBI) {
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Value *InVal = PN->removeIncomingValue(LatchBlock, false);
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// If this value was defined in the loop, take the value defined by the
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// last iteration of the loop.
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if (Instruction *InValI = dyn_cast<Instruction>(InVal)) {
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if (L->contains(InValI))
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InVal = LastValueMap[InVal];
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}
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PN->addIncoming(InVal, LastIterationBB);
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}
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}
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}
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// Now, if we're doing complete unrolling, loop over the PHI nodes in the
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// original block, setting them to their incoming values.
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if (CompletelyUnroll) {
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BasicBlock *Preheader = L->getLoopPreheader();
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for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) {
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PHINode *PN = OrigPHINode[i];
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// Loop over the PHI nodes in the original block, setting incoming values.
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for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) {
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PHINode *PN = OrigPHINode[i];
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if (CompletelyUnroll) {
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PN->replaceAllUsesWith(PN->getIncomingValueForBlock(Preheader));
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Header->getInstList().erase(PN);
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}
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else if (Count > 1) {
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Value *InVal = PN->removeIncomingValue(LatchBlock, false);
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// If this value was defined in the loop, take the value defined by the
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// last iteration of the loop.
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if (Instruction *InValI = dyn_cast<Instruction>(InVal)) {
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if (L->contains(InValI))
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InVal = LastValueMap[InVal];
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}
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assert(Latches.back() == LastValueMap[LatchBlock] && "bad last latch");
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PN->addIncoming(InVal, Latches.back());
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}
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}
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// Now that all the basic blocks for the unrolled iterations are in place,
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@ -355,6 +350,19 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
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// iteration.
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Term->setSuccessor(!ContinueOnTrue, Dest);
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} else {
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// Remove phi operands at this loop exit
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if (Dest != LoopExit) {
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BasicBlock *BB = Latches[i];
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for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
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SI != SE; ++SI) {
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if (*SI == Headers[i])
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continue;
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for (BasicBlock::iterator BBI = (*SI)->begin();
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PHINode *Phi = dyn_cast<PHINode>(BBI); ++BBI) {
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Phi->removeIncomingValue(BB, false);
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}
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}
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}
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// Replace the conditional branch with an unconditional one.
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BranchInst::Create(Dest, Term);
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Term->eraseFromParent();
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100
test/Transforms/LoopUnroll/2011-08-08-PhiUpdate.ll
Normal file
100
test/Transforms/LoopUnroll/2011-08-08-PhiUpdate.ll
Normal file
@ -0,0 +1,100 @@
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; RUN: opt < %s -loop-unroll -S -unroll-count=4 | FileCheck %s
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; Test phi update after partial unroll.
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declare i1 @check() nounwind
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; CHECK: @test
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; CHECK: if.else:
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; CHECK: if.then.loopexit
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; CHECK: %sub5.lcssa = phi i32 [ %sub{{.*}}, %if.else{{.*}} ], [ %sub{{.*}}, %if.else{{.*}} ], [ %sub{{.*}}, %if.else{{.*}} ], [ %sub{{.*}}, %if.else{{.*}} ]
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; CHECK: if.else.3
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define void @test1(i32 %i, i32 %j) nounwind uwtable ssp {
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entry:
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%cond1 = call zeroext i1 @check()
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br i1 %cond1, label %if.then, label %if.else.lr.ph
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if.else.lr.ph: ; preds = %entry
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br label %if.else
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if.else: ; preds = %if.else, %if.else.lr.ph
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%sub = phi i32 [ %i, %if.else.lr.ph ], [ %sub5, %if.else ]
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%sub5 = sub i32 %sub, %j
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%cond2 = call zeroext i1 @check()
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br i1 %cond2, label %if.then, label %if.else
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if.then: ; preds = %if.else, %entry
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%i.tr = phi i32 [ %i, %entry ], [ %sub5, %if.else ]
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ret void
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}
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; PR7318: assertion failure after doing a simple loop unroll
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;
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; CHECK: @test2
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; CHECK: bb1.bb2_crit_edge:
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; CHECK: %.lcssa = phi i32 [ %{{[2468]}}, %bb1{{.*}} ], [ %{{[2468]}}, %bb1{{.*}} ], [ %{{[2468]}}, %bb1{{.*}} ], [ %{{[2468]}}, %bb1{{.*}} ]
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; CHECK: bb1.3:
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define i32 @test2(i32* nocapture %p, i32 %n) nounwind readonly {
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entry:
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%0 = icmp sgt i32 %n, 0 ; <i1> [#uses=1]
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br i1 %0, label %bb.nph, label %bb2
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bb.nph: ; preds = %entry
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%tmp = zext i32 %n to i64 ; <i64> [#uses=1]
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br label %bb
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bb: ; preds = %bb.nph, %bb1
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%indvar = phi i64 [ 0, %bb.nph ], [ %indvar.next, %bb1 ] ; <i64> [#uses=2]
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%s.01 = phi i32 [ 0, %bb.nph ], [ %2, %bb1 ] ; <i32> [#uses=1]
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%scevgep = getelementptr i32* %p, i64 %indvar ; <i32*> [#uses=1]
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%1 = load i32* %scevgep, align 1 ; <i32> [#uses=1]
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%2 = add nsw i32 %1, %s.01 ; <i32> [#uses=2]
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br label %bb1
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bb1: ; preds = %bb
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%indvar.next = add i64 %indvar, 1 ; <i64> [#uses=2]
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%exitcond = icmp ne i64 %indvar.next, %tmp ; <i1> [#uses=1]
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br i1 %exitcond, label %bb, label %bb1.bb2_crit_edge
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bb1.bb2_crit_edge: ; preds = %bb1
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%.lcssa = phi i32 [ %2, %bb1 ] ; <i32> [#uses=1]
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br label %bb2
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bb2: ; preds = %bb1.bb2_crit_edge, %entry
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%s.0.lcssa = phi i32 [ %.lcssa, %bb1.bb2_crit_edge ], [ 0, %entry ] ; <i32> [#uses=1]
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ret i32 %s.0.lcssa
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}
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; Check phi update for loop with an early-exit.
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;
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; CHECK: @test3
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; CHECK: return.loopexit:
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; CHECK: %tmp7.i.lcssa = phi i32 [ %tmp7.i{{.*}}, %land.lhs.true{{.*}} ], [ %tmp7.i{{.*}}, %land.lhs.true{{.*}} ], [ %tmp7.i{{.*}}, %land.lhs.true{{.*}} ], [ %tmp7.i{{.*}}, %land.lhs.true{{.*}} ]
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; CHECK: exit.3:
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define i32 @test3() nounwind uwtable ssp align 2 {
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entry:
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br i1 undef, label %return, label %if.end
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if.end: ; preds = %entry
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br label %do.body
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do.body: ; preds = %do.cond, %if.end
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br i1 undef, label %exit, label %do.cond
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exit: ; preds = %do.body
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%tmp7.i = load i32* undef, align 8
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br i1 undef, label %do.cond, label %land.lhs.true
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land.lhs.true: ; preds = %exit
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br i1 undef, label %return, label %do.cond
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do.cond: ; preds = %land.lhs.true, %exit, %do.body
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br i1 undef, label %do.end, label %do.body
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do.end: ; preds = %do.cond
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br label %return
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return: ; preds = %do.end, %land.lhs.true, %entry
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%retval.0 = phi i32 [ 0, %do.end ], [ 0, %entry ], [ %tmp7.i, %land.lhs.true ]
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ret i32 %retval.0
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}
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62
test/Transforms/LoopUnroll/2011-08-09-PhiUpdate.ll
Normal file
62
test/Transforms/LoopUnroll/2011-08-09-PhiUpdate.ll
Normal file
@ -0,0 +1,62 @@
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; RUN: opt -S < %s -instcombine -inline -jump-threading -loop-unroll -unroll-count=4 | FileCheck %s
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;
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; This is a test case that required a number of setup passes because
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; it depends on block order.
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target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
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target triple = "x86_64-apple-macosx10.6.8"
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declare i1 @check() nounwind
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declare i32 @getval() nounwind
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; Check that the loop exit merges values from all the iterations. This
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; could be a tad fragile, but it's a good test.
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;
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; CHECK: @foo
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; CHECK: return:
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; CHECK: %retval.0 = phi i32 [ %tmp7.i, %land.lhs.true ], [ 0, %do.cond ], [ %tmp7.i.1, %land.lhs.true.1 ], [ 0, %do.cond.1 ], [ %tmp7.i.2, %land.lhs.true.2 ], [ 0, %do.cond.2 ], [ %tmp7.i.3, %land.lhs.true.3 ], [ 0, %do.cond.3 ]
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; CHECK-NOT: @bar
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; CHECK: bar.exit.3
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define i32 @foo() uwtable ssp align 2 {
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entry:
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br i1 undef, label %return, label %if.end
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if.end: ; preds = %entry
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%call2 = call i32 @getval()
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br label %do.body
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do.body: ; preds = %do.cond, %if.end
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%call6 = call i32 @bar()
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%cmp = icmp ne i32 %call6, 0
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br i1 %cmp, label %land.lhs.true, label %do.cond
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land.lhs.true: ; preds = %do.body
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%call10 = call i32 @getval()
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%cmp11 = icmp eq i32 0, %call10
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br i1 %cmp11, label %return, label %do.cond
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do.cond: ; preds = %land.lhs.true, %do.body
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%cmp18 = icmp sle i32 0, %call2
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br i1 %cmp18, label %do.body, label %return
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return: ; preds = %do.cond, %land.lhs.true, %entry
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%retval.0 = phi i32 [ 0, %entry ], [ %call6, %land.lhs.true ], [ 0, %do.cond ]
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ret i32 %retval.0
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}
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define linkonce_odr i32 @bar() nounwind uwtable ssp align 2 {
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entry:
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br i1 undef, label %land.lhs.true, label %cond.end
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land.lhs.true: ; preds = %entry
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%cmp4 = call zeroext i1 @check()
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br i1 %cmp4, label %cond.true, label %cond.end
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cond.true: ; preds = %land.lhs.true
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%tmp7 = call i32 @getval()
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br label %cond.end
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cond.end: ; preds = %cond.true, %land.lhs.true, %entry
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%cond = phi i32 [ %tmp7, %cond.true ], [ 0, %land.lhs.true ], [ 0, %entry ]
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ret i32 %cond
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}
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