[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

2 files changed, 38 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index e28c374549c..75677079e37 100644
--- a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -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(),
diff --git a/llvm/test/Transforms/LoopStrengthReduce/ARM/addrec-is-loop-invariant.ll b/llvm/test/Transforms/LoopStrengthReduce/ARM/addrec-is-loop-invariant.ll
new file mode 100644
index 00000000000..261c3cceed6
--- /dev/null
+++ b/llvm/test/Transforms/LoopStrengthReduce/ARM/addrec-is-loop-invariant.ll
@@ -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
+}