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Update domtree incrementally in loop peeling. 

With this change dominator tree remains in sync after each step of loop
peeling.

Differential Revision: https://reviews.llvm.org/D29029

llvm-svn: 292895
This commit is contained in:
Serge Pavlov 2017-01-24 06:58:39 +00:00
parent fc8798fa1b
commit 098ee2fe02
2 changed files with 31 additions and 8 deletions
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37
llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp
View File

@ -165,7 +165,8 @@ static void cloneLoopBlocks(Loop *L, unsigned IterNumber, BasicBlock *InsertTop,
BasicBlock *InsertBot, BasicBlock *Exit,
SmallVectorImpl<BasicBlock *> &NewBlocks,
LoopBlocksDFS &LoopBlocks, ValueToValueMapTy &VMap,
ValueToValueMapTy &LVMap, LoopInfo *LI) {
ValueToValueMapTy &LVMap, DominatorTree *DT,
LoopInfo *LI) {
BasicBlock *Header = L->getHeader();
BasicBlock *Latch = L->getLoopLatch();
@ -186,6 +187,17 @@ static void cloneLoopBlocks(Loop *L, unsigned IterNumber, BasicBlock *InsertTop,
ParentLoop->addBasicBlockToLoop(NewBB, *LI);
VMap[*BB] = NewBB;
// If dominator tree is available, insert nodes to represent cloned blocks.
if (DT) {
if (Header == *BB)
DT->addNewBlock(NewBB, InsertTop);
else {
DomTreeNode *IDom = DT->getNode(*BB)->getIDom();
// VMap must contain entry for IDom, as the iteration order is RPO.
DT->addNewBlock(NewBB, cast<BasicBlock>(VMap[IDom->getBlock()]));
}
}
}
// Hook-up the control flow for the newly inserted blocks.
@ -199,11 +211,13 @@ static void cloneLoopBlocks(Loop *L, unsigned IterNumber, BasicBlock *InsertTop,
// The backedge now goes to the "bottom", which is either the loop's real
// header (for the last peeled iteration) or the copied header of the next
// iteration (for every other iteration)
BranchInst *LatchBR =
cast<BranchInst>(cast<BasicBlock>(VMap[Latch])->getTerminator());
BasicBlock *NewLatch = cast<BasicBlock>(VMap[Latch]);
BranchInst *LatchBR = cast<BranchInst>(NewLatch->getTerminator());
unsigned HeaderIdx = (LatchBR->getSuccessor(0) == Header ? 0 : 1);
LatchBR->setSuccessor(HeaderIdx, InsertBot);
LatchBR->setSuccessor(1 - HeaderIdx, Exit);
if (DT)
DT->changeImmediateDominator(InsertBot, NewLatch);
// The new copy of the loop body starts with a bunch of PHI nodes
// that pick an incoming value from either the preheader, or the previous
@ -359,7 +373,19 @@ bool llvm::peelLoop(Loop *L, unsigned PeelCount, LoopInfo *LI,
CurHeaderWeight = 1;
cloneLoopBlocks(L, Iter, InsertTop, InsertBot, Exit,
NewBlocks, LoopBlocks, VMap, LVMap, LI);
NewBlocks, LoopBlocks, VMap, LVMap, DT, LI);
if (DT) {
// Latches of the cloned loops dominate over the loop exit, so idom of the
// latter is the first cloned loop body, as original PreHeader dominates
// the original loop body.
if (Iter == 0)
DT->changeImmediateDominator(Exit, cast<BasicBlock>(LVMap[Latch]));
#ifndef NDEBUG
if (VerifyDomInfo)
DT->verifyDomTree();
#endif
}
updateBranchWeights(InsertBot, cast<BranchInst>(VMap[LatchBR]), Iter,
PeelCount, ExitWeight);
@ -405,9 +431,6 @@ bool llvm::peelLoop(Loop *L, unsigned PeelCount, LoopInfo *LI,
LatchBR->setMetadata(LLVMContext::MD_prof, WeightNode);
}
// FIXME: Incrementally update domtree.
DT->recalculate(*L->getHeader()->getParent());
// If the loop is nested, we changed the parent loop, update SE.
if (Loop *ParentLoop = L->getParentLoop()) {
SE->forgetLoop(ParentLoop);

2
llvm/test/Transforms/LoopUnroll/peel-loop.ll
View File

@ -1,4 +1,4 @@
; RUN: opt < %s -S -loop-unroll -unroll-force-peel-count=3 -simplifycfg -instcombine | FileCheck %s
; RUN: opt < %s -S -loop-unroll -unroll-force-peel-count=3 -verify-dom-info -simplifycfg -instcombine | FileCheck %s
; Basic loop peeling - check that we can peel-off the first 3 loop iterations
; when explicitly requested.