From b1eede12818d91a32adac928c6fffcf6d2800dc0 Mon Sep 17 00:00:00 2001
From: Andrew Trick <atrick@apple.com>
Date: Wed, 10 Aug 2011 00:28:10 +0000
Subject: 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
---
lib/Transforms/Utils/LoopUnroll.cpp | 112 +++++++++++++++++++-----------------
1 file changed, 60 insertions(+), 52 deletions(-)
(limited to 'lib/Transforms')
diff --git a/lib/Transforms/Utils/LoopUnroll.cpp b/lib/Transforms/Utils/LoopUnroll.cpp
index fa508d4..f17098f 100644
--- a/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/lib/Transforms/Utils/LoopUnroll.cpp
@@ -21,6 +21,7 @@
#include "llvm/BasicBlock.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Analysis/LoopIterator.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Support/Debug.h"
@@ -225,11 +226,25 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
Headers.push_back(Header);
Latches.push_back(LatchBlock);
+ // The current on-the-fly SSA update requires blocks to be processed in
+ // reverse postorder so that LastValueMap contains the correct value at each
+ // exit.
+ LoopBlocksDFS DFS(L);
+ {
+ // Traverse the loop blocks using depth-first search to record RPO numbers
+ // for each block in the DFS result.
+ LoopBlocksTraversal Traversal(DFS, LI);
+ for (LoopBlocksTraversal::POTIterator POI = Traversal.begin(),
+ POE = Traversal.end(); POI != POE; ++POI);
+ }
+ // Stash the DFS iterators before adding blocks to the loop.
+ LoopBlocksDFS::RPOIterator BlockBegin = DFS.beginRPO();
+ LoopBlocksDFS::RPOIterator BlockEnd = DFS.endRPO();
+
for (unsigned It = 1; It != Count; ++It) {
std::vector<BasicBlock*> NewBlocks;
- for (std::vector<BasicBlock*>::iterator BB = LoopBlocks.begin(),
- E = LoopBlocks.end(); BB != E; ++BB) {
+ for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) {
ValueToValueMapTy VMap;
BasicBlock *New = CloneBasicBlock(*BB, VMap, "." + Twine(It));
Header->getParent()->getBasicBlockList().push_back(New);
@@ -255,35 +270,27 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
L->addBasicBlockToLoop(New, LI->getBase());
- // Add phi entries for newly created values to all exit blocks except
- // the successor of the latch block. The successor of the exit block will
- // be updated specially after unrolling all the way.
- if (*BB != LatchBlock)
- for (succ_iterator SI = succ_begin(*BB), SE = succ_end(*BB); SI != SE;
- ++SI)
- if (!L->contains(*SI))
- for (BasicBlock::iterator BBI = (*SI)->begin();
- PHINode *phi = dyn_cast<PHINode>(BBI); ++BBI) {
- Value *Incoming = phi->getIncomingValueForBlock(*BB);
- phi->addIncoming(Incoming, New);
- }
-
+ // Add phi entries for newly created values to all exit blocks.
+ for (succ_iterator SI = succ_begin(*BB), SE = succ_end(*BB);
+ SI != SE; ++SI) {
+ if (L->contains(*SI))
+ continue;
+ for (BasicBlock::iterator BBI = (*SI)->begin();
+ PHINode *phi = dyn_cast<PHINode>(BBI); ++BBI) {
+ Value *Incoming = phi->getIncomingValueForBlock(*BB);
+ ValueToValueMapTy::iterator It = LastValueMap.find(Incoming);
+ if (It != LastValueMap.end())
+ Incoming = It->second;
+ phi->addIncoming(Incoming, New);
+ }
+ }
// Keep track of new headers and latches as we create them, so that
// we can insert the proper branches later.
if (*BB == Header)
Headers.push_back(New);
- if (*BB == LatchBlock) {
+ if (*BB == LatchBlock)
Latches.push_back(New);
- // Also, clear out the new latch's back edge so that it doesn't look
- // like a new loop, so that it's amenable to being merged with adjacent
- // blocks later on.
- TerminatorInst *Term = New->getTerminator();
- assert(L->contains(Term->getSuccessor(!ContinueOnTrue)));
- assert(Term->getSuccessor(ContinueOnTrue) == LoopExit);
- Term->setSuccessor(!ContinueOnTrue, NULL);
- }
-
NewBlocks.push_back(New);
}
@@ -294,36 +301,24 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
::RemapInstruction(I, LastValueMap);
}
- // The latch block exits the loop. If there are any PHI nodes in the
- // successor blocks, update them to use the appropriate values computed as the
- // last iteration of the loop.
- if (Count != 1) {
- BasicBlock *LastIterationBB = cast<BasicBlock>(LastValueMap[LatchBlock]);
- for (succ_iterator SI = succ_begin(LatchBlock), SE = succ_end(LatchBlock);
- SI != SE; ++SI) {
- for (BasicBlock::iterator BBI = (*SI)->begin();
- PHINode *PN = dyn_cast<PHINode>(BBI); ++BBI) {
- Value *InVal = PN->removeIncomingValue(LatchBlock, false);
- // If this value was defined in the loop, take the value defined by the
- // last iteration of the loop.
- if (Instruction *InValI = dyn_cast<Instruction>(InVal)) {
- if (L->contains(InValI))
- InVal = LastValueMap[InVal];
- }
- PN->addIncoming(InVal, LastIterationBB);
- }
- }
- }
-
- // Now, if we're doing complete unrolling, loop over the PHI nodes in the
- // original block, setting them to their incoming values.
- if (CompletelyUnroll) {
- BasicBlock *Preheader = L->getLoopPreheader();
- for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) {
- PHINode *PN = OrigPHINode[i];
+ // Loop over the PHI nodes in the original block, setting incoming values.
+ for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) {
+ PHINode *PN = OrigPHINode[i];
+ if (CompletelyUnroll) {
PN->replaceAllUsesWith(PN->getIncomingValueForBlock(Preheader));
Header->getInstList().erase(PN);
}
+ else if (Count > 1) {
+ Value *InVal = PN->removeIncomingValue(LatchBlock, false);
+ // If this value was defined in the loop, take the value defined by the
+ // last iteration of the loop.
+ if (Instruction *InValI = dyn_cast<Instruction>(InVal)) {
+ if (L->contains(InValI))
+ InVal = LastValueMap[InVal];
+ }
+ assert(Latches.back() == LastValueMap[LatchBlock] && "bad last latch");
+ PN->addIncoming(InVal, Latches.back());
+ }
}
// Now that all the basic blocks for the unrolled iterations are in place,
@@ -355,6 +350,19 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
// iteration.
Term->setSuccessor(!ContinueOnTrue, Dest);
} else {
+ // Remove phi operands at this loop exit
+ if (Dest != LoopExit) {
+ BasicBlock *BB = Latches[i];
+ for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
+ SI != SE; ++SI) {
+ if (*SI == Headers[i])
+ continue;
+ for (BasicBlock::iterator BBI = (*SI)->begin();
+ PHINode *Phi = dyn_cast<PHINode>(BBI); ++BBI) {
+ Phi->removeIncomingValue(BB, false);
+ }
+ }
+ }
// Replace the conditional branch with an unconditional one.
BranchInst::Create(Dest, Term);
Term->eraseFromParent();
--
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