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LSR should avoid redundant edge splitting.

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This handles the case in which LSR rewrites an IV user that is a phi and
splits critical edges originating from a switch.
Fixes <rdar://problem/6453893> LSR is not splitting edges "nicely"


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141059 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrew Trick 2011-10-04 03:50:44 +00:00
parent 2aeb8027d6
commit f143b79b78
4 changed files with 55 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
include/llvm/Transforms/Utils/BasicBlockUtils.h
View File

@ -109,7 +109,8 @@ bool isCriticalEdge(const TerminatorInst *TI, unsigned SuccNum,
/// to.
///
BasicBlock *SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum,
Pass *P = 0, bool MergeIdenticalEdges = false);
Pass *P = 0, bool MergeIdenticalEdges = false,
bool DontDeleteUselessPHIs = false);
inline BasicBlock *SplitCriticalEdge(BasicBlock *BB, succ_iterator SI,
Pass *P = 0) {
@ -136,13 +137,15 @@ inline bool SplitCriticalEdge(BasicBlock *Succ, pred_iterator PI, Pass *P = 0) {
/// described above.
inline BasicBlock *SplitCriticalEdge(BasicBlock *Src, BasicBlock *Dst,
Pass *P = 0,
bool MergeIdenticalEdges = false) {
bool MergeIdenticalEdges = false,
bool DontDeleteUselessPHIs = false) {
TerminatorInst *TI = Src->getTerminator();
unsigned i = 0;
while (1) {
assert(i != TI->getNumSuccessors() && "Edge doesn't exist!");
if (TI->getSuccessor(i) == Dst)
return SplitCriticalEdge(TI, i, P, MergeIdenticalEdges);
return SplitCriticalEdge(TI, i, P, MergeIdenticalEdges,
DontDeleteUselessPHIs);
++i;
}
}

4
lib/Transforms/Scalar/LoopStrengthReduce.cpp
View File

@ -3677,7 +3677,9 @@ void LSRInstance::RewriteForPHI(PHINode *PN,
// Split the critical edge.
BasicBlock *NewBB = 0;
if (!Parent->isLandingPad()) {
NewBB = SplitCriticalEdge(BB, Parent, P);
NewBB = SplitCriticalEdge(BB, Parent, P,
/*MergeIdenticalEdges=*/true,
/*DontDeleteUselessPhis=*/true);
} else {
SmallVector<BasicBlock*, 2> NewBBs;
SplitLandingPadPredecessors(Parent, BB, "", "", P, NewBBs);

5
lib/Transforms/Utils/BreakCriticalEdges.cpp
View File

@ -167,7 +167,8 @@ static void CreatePHIsForSplitLoopExit(SmallVectorImpl<BasicBlock *> &Preds,
/// to.
///
BasicBlock *llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum,
Pass *P, bool MergeIdenticalEdges) {
Pass *P, bool MergeIdenticalEdges,
bool DontDeleteUselessPhis) {
if (!isCriticalEdge(TI, SuccNum, MergeIdenticalEdges)) return 0;
assert(!isa<IndirectBrInst>(TI) &&
@ -224,7 +225,7 @@ BasicBlock *llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum,
if (TI->getSuccessor(i) != DestBB) continue;
// Remove an entry for TIBB from DestBB phi nodes.
DestBB->removePredecessor(TIBB);
DestBB->removePredecessor(TIBB, DontDeleteUselessPhis);
// We found another edge to DestBB, go to NewBB instead.
TI->setSuccessor(i, NewBB);

43
test/Transforms/LoopStrengthReduce/2011-10-03-CritEdgeMerge.ll Normal file
View File

@ -0,0 +1,43 @@
; RUN: opt -loop-reduce -S < %s | FileCheck %s
;
; Test LSR's use of SplitCriticalEdge during phi rewriting.
; Verify that identical edges are merged. rdar://problem/6453893
target triple = "x86-apple-darwin"
; CHECK: @test
; CHECK: bb89:
; CHECK: phi i8* [ %lsr.iv.next1, %bbA.bb89_crit_edge ], [ %lsr.iv.next1, %bbB.bb89_crit_edge ]{{$}}
define i8* @test() {
entry:
br label %loop
loop:
%rec = phi i32 [ %next, %loop ], [ 0, %entry ]
%next = add i32 %rec, 1
%tmp75 = getelementptr i8* null, i32 %next
br i1 false, label %loop, label %loopexit
loopexit:
br i1 false, label %bbA, label %bbB
bbA:
switch i32 0, label %bb89 [
i32 47, label %bb89
i32 58, label %bb89
]
bbB:
switch i8 0, label %bb89 [
i8 47, label %bb89
i8 58, label %bb89
]
bb89:
%tmp75phi = phi i8* [ %tmp75, %bbA ], [ %tmp75, %bbA ], [ %tmp75, %bbA ], [ %tmp75, %bbB ], [ %tmp75, %bbB ], [ %tmp75, %bbB ]
br label %exit
exit:
ret i8* %tmp75phi
}