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[SimplifyCFG] Teach merge conditional stores to handle cases where the PostBB has more than 2 predecessors by inserting a new block for the store. 

Summary:
Currently merge conditional stores can't handle cases where PostBB (the block we need to move the store to) has more than 2 predecessors.

This patch removes that restriction by creating a new block with only the 2 predecessors we care about and an unconditional branch to the original block. This provides a place to put the store.

Reviewers: efriedma, jmolloy, ABataev

Reviewed By: efriedma

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D39760

llvm-svn: 329142
This commit is contained in:
Craig Topper 2018-04-04 03:47:17 +00:00
parent 8427e94b54
commit 7d3aba6687
2 changed files with 55 additions and 1 deletions
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17
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -2982,6 +2982,21 @@ static bool mergeConditionalStoreToAddress(BasicBlock *PTB, BasicBlock *PFB,
if (&*I != PStore && I->mayReadOrWriteMemory())
return false;
// If PostBB has more than two predecessors, we need to split it so we can
// sink the store.
if (std::next(pred_begin(PostBB), 2) != pred_end(PostBB)) {
// We know that QFB's only successor is PostBB. And QFB has a single
// predecessor. If QTB exists, then its only successor is also PostBB.
// If QTB does not exist, then QFB's only predecessor has a conditional
// branch to QFB and PostBB.
BasicBlock *TruePred = QTB ? QTB : QFB->getSinglePredecessor();
BasicBlock *NewBB = SplitBlockPredecessors(PostBB, { QFB, TruePred},
"condstore.split");
if (!NewBB)
return false;
PostBB = NewBB;
}
// OK, we're going to sink the stores to PostBB. The store has to be
// conditional though, so first create the predicate.
Value *PCond = cast<BranchInst>(PFB->getSinglePredecessor()->getTerminator())
@ -3117,7 +3132,7 @@ static bool mergeConditionalStores(BranchInst *PBI, BranchInst *QBI,
if ((PTB && !HasOnePredAndOneSucc(PTB, PBI->getParent(), QBI->getParent())) ||
(QTB && !HasOnePredAndOneSucc(QTB, QBI->getParent(), PostBB)))
return false;
if (!PostBB->hasNUses(2) || !QBI->getParent()->hasNUses(2))
if (!QBI->getParent()->hasNUses(2))
return false;
// OK, this is a sequence of two diamonds or triangles.

39
llvm/test/Transforms/SimplifyCFG/merge-cond-stores.ll
View File

@ -369,3 +369,42 @@ end:
%z4 = phi i32 [ %z3, %no2 ], [ 3, %yes2 ]
ret i32 %z4
}
; This test has an outer if over the two triangles. This requires creating a new BB to hold the store.
define void @test_outer_if(i32* %p, i32 %a, i32 %b, i32 %c) {
; CHECK-LABEL: @test_outer_if(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[X3:%.*]] = icmp eq i32 [[C:%.*]], 0
; CHECK-NEXT: br i1 [[X3]], label [[END:%.*]], label [[CONTINUE:%.*]]
; CHECK: continue:
; CHECK-NEXT: [[X1:%.*]] = icmp ne i32 [[A:%.*]], 0
; CHECK-NEXT: [[X2:%.*]] = icmp eq i32 [[B:%.*]], 0
; CHECK-NEXT: [[TMP0:%.*]] = xor i1 [[X2]], true
; CHECK-NEXT: [[TMP1:%.*]] = or i1 [[X1]], [[TMP0]]
; CHECK-NEXT: br i1 [[TMP1]], label [[TMP2:%.*]], label [[END]]
; CHECK: [[NOT_X2:%.*]] = xor i1 [[X2]], true
; CHECK-NEXT: [[SPEC_SELECT:%.*]] = zext i1 [[NOT_X2]] to i32
; CHECK-NEXT: store i32 [[SPEC_SELECT]], i32* [[P:%.*]], align 4
; CHECK-NEXT: br label [[END]]
; CHECK: end:
; CHECK-NEXT: ret void
;
entry:
%x3 = icmp eq i32 %c, 0
br i1 %x3, label %end, label %continue
continue:
%x1 = icmp eq i32 %a, 0
br i1 %x1, label %fallthrough, label %yes1
yes1:
store i32 0, i32* %p
br label %fallthrough
fallthrough:
%x2 = icmp eq i32 %b, 0
br i1 %x2, label %end, label %yes2
yes2:
store i32 1, i32* %p
br label %end
end:
ret void
}