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[ARM] Loop Strength Reduction crashes when targeting ARM or Thumb. 

Scalar Evolution asserts when not all the operands of an Add Recurrence
Expression are loop invariants. Loop Strength Reduction should only
create affine Add Recurrences, so that both the start and the step of
the expression are loop invariants.

Differential Revision: https://reviews.llvm.org/D26185

llvm-svn: 286347
This commit is contained in:
Alexandros Lamprineas 2016-11-09 08:53:07 +00:00
parent 8530137de5
commit 0ee3ec2fe4
2 changed files with 38 additions and 3 deletions
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6
llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
View File

@ -325,7 +325,7 @@ static void DoInitialMatch(const SCEV *S, Loop *L,
// Look at addrec operands.
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S))
if (!AR->getStart()->isZero()) {
if (!AR->getStart()->isZero() && AR->isAffine()) {
DoInitialMatch(AR->getStart(), L, Good, Bad, SE);
DoInitialMatch(SE.getAddRecExpr(SE.getConstant(AR->getType(), 0),
AR->getStepRecurrence(SE),
@ -568,7 +568,7 @@ static const SCEV *getExactSDiv(const SCEV *LHS, const SCEV *RHS,
// Distribute the sdiv over addrec operands, if the addrec doesn't overflow.
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(LHS)) {
if (IgnoreSignificantBits || isAddRecSExtable(AR, SE)) {
if ((IgnoreSignificantBits || isAddRecSExtable(AR, SE)) && AR->isAffine()) {
const SCEV *Step = getExactSDiv(AR->getStepRecurrence(SE), RHS, SE,
IgnoreSignificantBits);
if (!Step) return nullptr;
@ -3196,7 +3196,7 @@ static const SCEV *CollectSubexprs(const SCEV *S, const SCEVConstant *C,
return nullptr;
} else if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
// Split a non-zero base out of an addrec.
if (AR->getStart()->isZero())
if (AR->getStart()->isZero() || !AR->isAffine())
return S;
const SCEV *Remainder = CollectSubexprs(AR->getStart(),

35
llvm/test/Transforms/LoopStrengthReduce/ARM/addrec-is-loop-invariant.ll Normal file
View File

@ -0,0 +1,35 @@
; RUN: llc -mtriple=armv8-eabi -verify-machineinstrs %s -o /dev/null
; This test ensures that Loop Strength Reduction will
; not create an Add Reccurence Expression if not all
; its operands are loop invariants.
define void @add_rec_expr() {
entry:
br label %loop0
loop0:
%c.0 = phi i32 [ 0, %entry ], [ %inc.0, %loop0 ]
%inc.0 = add nuw i32 %c.0, 1
br i1 undef, label %loop0, label %bb1
bb1:
%mul.0 = mul i32 %c.0, %c.0
%gelptr.0 = getelementptr inbounds i16, i16* undef, i32 %mul.0
br label %loop1
loop1:
%inc.1 = phi i32 [ %inc.2, %bb4 ], [ 0, %bb1 ]
%mul.1 = mul i32 %inc.1, %c.0
br label %bb3
bb3:
%add.0 = add i32 undef, %mul.1
%gelptr.1 = getelementptr inbounds i16, i16* %gelptr.0, i32 %add.0
store i16 undef, i16* %gelptr.1, align 2
br label %bb4
bb4:
%inc.2 = add nuw i32 %inc.1, 1
br label %loop1
}