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[InstCombine] Properly change GEP type when reassociating loop invari…
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…ant GEP chains

Summary:
This is a fix to PR37005.

Essentially, rL328539 ([InstCombine] reassociate loop invariant GEP chains to enable LICM) contains a bug
whereby it will convert:
%src = getelementptr inbounds i8, i8* %base, <2 x i64> %val
%res = getelementptr inbounds i8, <2 x i8*> %src, i64 %val2
into:
%src = getelementptr inbounds i8, i8* %base, i64 %val2
%res = getelementptr inbounds i8, <2 x i8*> %src, <2 x i64> %val

By swapping the index operands if the GEPs are in a loop, and %val is loop variant while %val2
is loop invariant.

This fix recreates new GEP instructions if the index operand swap would result in the type
of %src changing from vector to scalar, or vice versa.

Reviewers: sebpop, spatel

Reviewed By: sebpop

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D45287

llvm-svn: 329331
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Daniel Neilson committed Apr 5, 2018
1 parent 9eec202 commit 367c2ae
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Showing 2 changed files with 133 additions and 3 deletions.
39 changes: 36 additions & 3 deletions llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
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Expand Up @@ -1680,9 +1680,42 @@ Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
// invariant: this breaks the dependence between GEPs and allows LICM
// to hoist the invariant part out of the loop.
if (L->isLoopInvariant(GO1) && !L->isLoopInvariant(SO1)) {
Src->setOperand(1, GO1);
GEP.setOperand(1, SO1);
return &GEP;
// We have to be careful here.
// We have something like:
// %src = getelementptr <ty>, <ty>* %base, <ty> %idx
// %gep = getelementptr <ty>, <ty>* %src, <ty> %idx2
// If we just swap idx & idx2 then we could inadvertantly
// change %src from a vector to a scalar, or vice versa.
// Cases:
// 1) %base a scalar & idx a scalar & idx2 a vector
// => Swapping idx & idx2 turns %src into a vector type.
// 2) %base a scalar & idx a vector & idx2 a scalar
// => Swapping idx & idx2 turns %src in a scalar type
// 3) %base, %idx, and %idx2 are scalars
// => %src & %gep are scalars
// => swapping idx & idx2 is safe
// 4) %base a vector
// => %src is a vector
// => swapping idx & idx2 is safe.
auto *SO0 = Src->getOperand(0);
auto *SO0Ty = SO0->getType();
if (!isa<VectorType>(GEPType) || // case 3
isa<VectorType>(SO0Ty)) { // case 4
Src->setOperand(1, GO1);
GEP.setOperand(1, SO1);
return &GEP;
} else {
// Case 1 or 2
// -- have to recreate %src & %gep
// put NewSrc at same location as %src
Builder.SetInsertPoint(cast<Instruction>(PtrOp));
auto *NewSrc = cast<GetElementPtrInst>(
Builder.CreateGEP(SO0, GO1, Src->getName()));
NewSrc->setIsInBounds(Src->isInBounds());
auto *NewGEP = GetElementPtrInst::Create(nullptr, NewSrc, {SO1});
NewGEP->setIsInBounds(GEP.isInBounds());
return NewGEP;
}
}
}
}
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97 changes: 97 additions & 0 deletions llvm/test/Transforms/InstCombine/gep-combine-loop-invariant.ll
View file
Expand Up @@ -88,3 +88,100 @@ do.end: ; preds = %do.body, %land.lhs.
%cont.0 = phi i32 [ 1, %entry ], [ 0, %if.then ], [ 0, %land.lhs.true ], [ 1, %do.body ]
ret i32 %cont.0
}

declare void @blackhole(<2 x i8*>)

define void @PR37005(i8* %base, i8** %in) {
; CHECK-LABEL: @PR37005(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[E2:%.*]] = getelementptr inbounds i8*, i8** [[IN:%.*]], i64 undef
; CHECK-NEXT: [[E4:%.*]] = getelementptr inbounds i8*, i8** [[E2]], <2 x i64> <i64 0, i64 1>
; CHECK-NEXT: [[PI1:%.*]] = ptrtoint <2 x i8**> [[E4]] to <2 x i64>
; CHECK-NEXT: [[LR1:%.*]] = lshr <2 x i64> [[PI1]], <i64 21, i64 21>
; CHECK-NEXT: [[SL1:%.*]] = shl nuw nsw <2 x i64> [[LR1]], <i64 7, i64 7>
; CHECK-NEXT: [[E51:%.*]] = getelementptr inbounds i8, i8* [[BASE:%.*]], i64 80
; CHECK-NEXT: [[E6:%.*]] = getelementptr inbounds i8, i8* [[E51]], <2 x i64> [[SL1]]
; CHECK-NEXT: call void @blackhole(<2 x i8*> [[E6]])
; CHECK-NEXT: br label [[LOOP]]
;
entry:
br label %loop

loop:
%e1 = getelementptr inbounds i8*, i8** %in, i64 undef
%e2 = getelementptr inbounds i8*, i8** %e1, i64 6
%bc1 = bitcast i8** %e2 to <2 x i8*>*
%e3 = getelementptr inbounds <2 x i8*>, <2 x i8*>* %bc1, i64 0, i64 0
%e4 = getelementptr inbounds i8*, i8** %e3, <2 x i64> <i64 0, i64 1>
%pi1 = ptrtoint <2 x i8**> %e4 to <2 x i64>
%lr1 = lshr <2 x i64> %pi1, <i64 21, i64 21>
%sl1 = shl nuw nsw <2 x i64> %lr1, <i64 7, i64 7>
%e5 = getelementptr inbounds i8, i8* %base, <2 x i64> %sl1
%e6 = getelementptr inbounds i8, <2 x i8*> %e5, i64 80
call void @blackhole(<2 x i8*> %e6)
br label %loop
}

define void @PR37005_2(i8* %base, i8** %in) {
; CHECK-LABEL: @PR37005_2(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[E2:%.*]] = getelementptr inbounds i8*, i8** [[IN:%.*]], i64 undef
; CHECK-NEXT: [[PI1:%.*]] = ptrtoint i8** [[E2]] to i64
; CHECK-NEXT: [[LR1:%.*]] = lshr i64 [[PI1]], 21
; CHECK-NEXT: [[SL1:%.*]] = shl nuw nsw i64 [[LR1]], 7
; CHECK-NEXT: [[E51:%.*]] = getelementptr inbounds i8, i8* [[BASE:%.*]], <2 x i64> <i64 80, i64 60>
; CHECK-NEXT: [[E6:%.*]] = getelementptr inbounds i8, <2 x i8*> [[E51]], i64 [[SL1]]
; CHECK-NEXT: call void @blackhole(<2 x i8*> [[E6]])
; CHECK-NEXT: br label [[LOOP]]
;
entry:
br label %loop

loop:
%e1 = getelementptr inbounds i8*, i8** %in, i64 undef
%e2 = getelementptr inbounds i8*, i8** %e1, i64 6
%pi1 = ptrtoint i8** %e2 to i64
%lr1 = lshr i64 %pi1, 21
%sl1 = shl nuw nsw i64 %lr1, 7
%e5 = getelementptr inbounds i8, i8* %base, i64 %sl1
%e6 = getelementptr inbounds i8, i8* %e5, <2 x i64> <i64 80, i64 60>
call void @blackhole(<2 x i8*> %e6)
br label %loop
}

define void @PR37005_3(<2 x i8*> %base, i8** %in) {
; CHECK-LABEL: @PR37005_3(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[E2:%.*]] = getelementptr inbounds i8*, i8** [[IN:%.*]], i64 undef
; CHECK-NEXT: [[E4:%.*]] = getelementptr inbounds i8*, i8** [[E2]], <2 x i64> <i64 0, i64 1>
; CHECK-NEXT: [[PI1:%.*]] = ptrtoint <2 x i8**> [[E4]] to <2 x i64>
; CHECK-NEXT: [[LR1:%.*]] = lshr <2 x i64> [[PI1]], <i64 21, i64 21>
; CHECK-NEXT: [[SL1:%.*]] = shl nuw nsw <2 x i64> [[LR1]], <i64 7, i64 7>
; CHECK-NEXT: [[E5:%.*]] = getelementptr inbounds i8, <2 x i8*> [[BASE:%.*]], i64 80
; CHECK-NEXT: [[E6:%.*]] = getelementptr inbounds i8, <2 x i8*> [[E5]], <2 x i64> [[SL1]]
; CHECK-NEXT: call void @blackhole(<2 x i8*> [[E6]])
; CHECK-NEXT: br label [[LOOP]]
;
entry:
br label %loop

loop:
%e1 = getelementptr inbounds i8*, i8** %in, i64 undef
%e2 = getelementptr inbounds i8*, i8** %e1, i64 6
%bc1 = bitcast i8** %e2 to <2 x i8*>*
%e3 = getelementptr inbounds <2 x i8*>, <2 x i8*>* %bc1, i64 0, i64 0
%e4 = getelementptr inbounds i8*, i8** %e3, <2 x i64> <i64 0, i64 1>
%pi1 = ptrtoint <2 x i8**> %e4 to <2 x i64>
%lr1 = lshr <2 x i64> %pi1, <i64 21, i64 21>
%sl1 = shl nuw nsw <2 x i64> %lr1, <i64 7, i64 7>
%e5 = getelementptr inbounds i8, <2 x i8*> %base, <2 x i64> %sl1
%e6 = getelementptr inbounds i8, <2 x i8*> %e5, i64 80
call void @blackhole(<2 x i8*> %e6)
br label %loop
}

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