[llvm-commits] [llvm] r123077 - /llvm/trunk/lib/Transforms/Scalar/LoopRotation.cpp
Chris Lattner
sabre at nondot.org
Sat Jan 8 11:26:33 PST 2011
Author: lattner
Date: Sat Jan 8 13:26:33 2011
New Revision: 123077
URL: http://llvm.org/viewvc/llvm-project?rev=123077&view=rev
Log:
split ssa updating code out to its own helper function. Don't bother
moving the OrigHeader block anymore: we just merge it away anyway so
its code layout doesn't matter.
Modified:
llvm/trunk/lib/Transforms/Scalar/LoopRotation.cpp
Modified: llvm/trunk/lib/Transforms/Scalar/LoopRotation.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopRotation.cpp?rev=123077&r1=123076&r2=123077&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopRotation.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopRotation.cpp Sat Jan 8 13:26:33 2011
@@ -80,6 +80,71 @@
return MadeChange;
}
+/// RewriteUsesOfClonedInstructions - We just cloned the instructions from the
+/// old header into the preheader. If there were uses of the values produced by
+/// these instruction that were outside of the loop, we have to insert PHI nodes
+/// to merge the two values. Do this now.
+static void RewriteUsesOfClonedInstructions(BasicBlock *OrigHeader,
+ BasicBlock *OrigPreheader,
+ ValueToValueMapTy &ValueMap) {
+ // Remove PHI node entries that are no longer live.
+ BasicBlock::iterator I, E = OrigHeader->end();
+ for (I = OrigHeader->begin(); PHINode *PN = dyn_cast<PHINode>(I); ++I)
+ PN->removeIncomingValue(PN->getBasicBlockIndex(OrigPreheader));
+
+ // Now fix up users of the instructions in OrigHeader, inserting PHI nodes
+ // as necessary.
+ SSAUpdater SSA;
+ for (I = OrigHeader->begin(); I != E; ++I) {
+ Value *OrigHeaderVal = I;
+
+ // If there are no uses of the value (e.g. because it returns void), there
+ // is nothing to rewrite.
+ if (OrigHeaderVal->use_empty())
+ continue;
+
+ Value *OrigPreHeaderVal = ValueMap[OrigHeaderVal];
+
+ // The value now exits in two versions: the initial value in the preheader
+ // and the loop "next" value in the original header.
+ SSA.Initialize(OrigHeaderVal->getType(), OrigHeaderVal->getName());
+ SSA.AddAvailableValue(OrigHeader, OrigHeaderVal);
+ SSA.AddAvailableValue(OrigPreheader, OrigPreHeaderVal);
+
+ // Visit each use of the OrigHeader instruction.
+ for (Value::use_iterator UI = OrigHeaderVal->use_begin(),
+ UE = OrigHeaderVal->use_end(); UI != UE; ) {
+ // Grab the use before incrementing the iterator.
+ Use &U = UI.getUse();
+
+ // Increment the iterator before removing the use from the list.
+ ++UI;
+
+ // SSAUpdater can't handle a non-PHI use in the same block as an
+ // earlier def. We can easily handle those cases manually.
+ Instruction *UserInst = cast<Instruction>(U.getUser());
+ if (!isa<PHINode>(UserInst)) {
+ BasicBlock *UserBB = UserInst->getParent();
+
+ // The original users in the OrigHeader are already using the
+ // original definitions.
+ if (UserBB == OrigHeader)
+ continue;
+
+ // Users in the OrigPreHeader need to use the value to which the
+ // original definitions are mapped.
+ if (UserBB == OrigPreheader) {
+ U = OrigPreHeaderVal;
+ continue;
+ }
+ }
+
+ // Anything else can be handled by SSAUpdater.
+ SSA.RewriteUse(U);
+ }
+ }
+}
+
/// Rotate loop LP. Return true if the loop is rotated.
bool LoopRotate::rotateLoop(Loop *L) {
// If the loop has only one block then there is not much to rotate.
@@ -116,9 +181,9 @@
}
// Now, this loop is suitable for rotation.
- BasicBlock *OrigPreHeader = L->getLoopPreheader();
+ BasicBlock *OrigPreheader = L->getLoopPreheader();
BasicBlock *OrigLatch = L->getLoopLatch();
- assert(OrigPreHeader && OrigLatch && "Loop not in canonical form?");
+ assert(OrigPreheader && OrigLatch && "Loop not in canonical form?");
// Anything ScalarEvolution may know about this loop or the PHI nodes
// in its header will soon be invalidated.
@@ -150,11 +215,11 @@
// For PHI nodes, the value available in OldPreHeader is just the
// incoming value from OldPreHeader.
for (; PHINode *PN = dyn_cast<PHINode>(I); ++I)
- ValueMap[PN] = PN->getIncomingValue(PN->getBasicBlockIndex(OrigPreHeader));
+ ValueMap[PN] = PN->getIncomingValue(PN->getBasicBlockIndex(OrigPreheader));
// For the rest of the instructions, either hoist to the OrigPreheader if
// possible or create a clone in the OldPreHeader if not.
- TerminatorInst *LoopEntryBranch = OrigPreHeader->getTerminator();
+ TerminatorInst *LoopEntryBranch = OrigPreheader->getTerminator();
while (I != E) {
Instruction *Inst = I++;
@@ -202,90 +267,28 @@
for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
for (BasicBlock::iterator BI = TI->getSuccessor(i)->begin();
PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
- PN->addIncoming(PN->getIncomingValueForBlock(OrigHeader), OrigPreHeader);
+ PN->addIncoming(PN->getIncomingValueForBlock(OrigHeader), OrigPreheader);
// Now that OrigPreHeader has a clone of OrigHeader's terminator, remove
// OrigPreHeader's old terminator (the original branch into the loop), and
// remove the corresponding incoming values from the PHI nodes in OrigHeader.
LoopEntryBranch->eraseFromParent();
- for (I = OrigHeader->begin(); PHINode *PN = dyn_cast<PHINode>(I); ++I)
- PN->removeIncomingValue(PN->getBasicBlockIndex(OrigPreHeader));
-
- // Now fix up users of the instructions in OrigHeader, inserting PHI nodes
- // as necessary.
- SSAUpdater SSA;
- for (I = OrigHeader->begin(); I != E; ++I) {
- Value *OrigHeaderVal = I;
- Value *OrigPreHeaderVal = ValueMap[OrigHeaderVal];
-
- // If there are no uses of the value (e.g. because it returns void), there
- // is nothing to rewrite.
- if (OrigHeaderVal->use_empty() && OrigPreHeaderVal->use_empty())
- continue;
-
- // The value now exits in two versions: the initial value in the preheader
- // and the loop "next" value in the original header.
- SSA.Initialize(OrigHeaderVal->getType(), OrigHeaderVal->getName());
- SSA.AddAvailableValue(OrigHeader, OrigHeaderVal);
- SSA.AddAvailableValue(OrigPreHeader, OrigPreHeaderVal);
-
- // Visit each use of the OrigHeader instruction.
- for (Value::use_iterator UI = OrigHeaderVal->use_begin(),
- UE = OrigHeaderVal->use_end(); UI != UE; ) {
- // Grab the use before incrementing the iterator.
- Use &U = UI.getUse();
-
- // Increment the iterator before removing the use from the list.
- ++UI;
- // SSAUpdater can't handle a non-PHI use in the same block as an
- // earlier def. We can easily handle those cases manually.
- Instruction *UserInst = cast<Instruction>(U.getUser());
- if (!isa<PHINode>(UserInst)) {
- BasicBlock *UserBB = UserInst->getParent();
-
- // The original users in the OrigHeader are already using the
- // original definitions.
- if (UserBB == OrigHeader)
- continue;
-
- // Users in the OrigPreHeader need to use the value to which the
- // original definitions are mapped.
- if (UserBB == OrigPreHeader) {
- U = OrigPreHeaderVal;
- continue;
- }
- }
-
- // Anything else can be handled by SSAUpdater.
- SSA.RewriteUse(U);
- }
- }
+ // If there were any uses of instructions in the duplicated block outside the
+ // loop, update them, inserting PHI nodes as required
+ RewriteUsesOfClonedInstructions(OrigHeader, OrigPreheader, ValueMap);
// NewHeader is now the header of the loop.
L->moveToHeader(NewHeader);
assert(L->getHeader() == NewHeader && "Latch block is our new header");
- // Move the original header to the bottom of the loop, where it now more
- // naturally belongs. This isn't necessary for correctness, and CodeGen can
- // usually reorder blocks on its own to fix things like this up, but it's
- // still nice to keep the IR readable.
- //
- // The original header should have only one predecessor at this point, since
- // we checked that the loop had a proper preheader and unique backedge before
- // we started.
- assert(OrigHeader->getSinglePredecessor() &&
- "Original loop header has too many predecessors after loop rotation!");
- OrigHeader->moveAfter(OrigHeader->getSinglePredecessor());
-
-
// Update DominatorTree to reflect the CFG change we just made. Then split
// edges as necessary to preserve LoopSimplify form.
if (DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>()) {
// Since OrigPreheader now has the conditional branch to Exit block, it is
// the dominator of Exit.
- DT->changeImmediateDominator(Exit, OrigPreHeader);
- DT->changeImmediateDominator(NewHeader, OrigPreHeader);
+ DT->changeImmediateDominator(Exit, OrigPreheader);
+ DT->changeImmediateDominator(NewHeader, OrigPreheader);
// Update OrigHeader to be dominated by the new header block.
DT->changeImmediateDominator(OrigHeader, OrigLatch);
@@ -293,12 +296,13 @@
// Right now OrigPreHeader has two successors, NewHeader and ExitBlock, and
// thus is not a preheader anymore. Split the edge to form a real preheader.
- BasicBlock *NewPH = SplitCriticalEdge(OrigPreHeader, NewHeader, this);
+ BasicBlock *NewPH = SplitCriticalEdge(OrigPreheader, NewHeader, this);
NewPH->setName(NewHeader->getName() + ".lr.ph");
// Preserve canonical loop form, which means that 'Exit' should have only one
// predecessor.
- SplitCriticalEdge(L->getLoopLatch(), Exit, this);
+ BasicBlock *ExitSplit = SplitCriticalEdge(L->getLoopLatch(), Exit, this);
+ ExitSplit->moveBefore(Exit);
assert(L->getLoopPreheader() == NewPH &&
"Invalid loop preheader after loop rotation");
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