[LV] Emitting SCEV checks with OptForSize

When optimising for size and SCEV runtime checks need to be emitted to check
overflow behaviour, the loop vectorizer can run in this assert:

  LoopVectorize.cpp:2699: void llvm::InnerLoopVectorizer::emitSCEVChecks(
  llvm::Loop *, llvm::BasicBlock *): Assertion `!BB->getParent()->hasOptSize()
  && "Cannot SCEV check stride or overflow when opt

We should not generate predicates while optimising for size because
code will be generated for predicates such as these SCEV overflow runtime
checks.

This should fix PR43371.

Differential Revision: https://reviews.llvm.org/D68082

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@374166 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp b/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
index 9731abbb50aafc01bdb2350363bb12261f6621d1..0a20ab71dfaaa917fd6d72f7f0bd98e8ee3dad9f 100644 (file)
--- a/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
+++ b/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
@@ -409,7 +409,8 @@ int LoopVectorizationLegality::isConsecutivePtr(Value *Ptr) {
   const ValueToValueMap &Strides =
       getSymbolicStrides() ? *getSymbolicStrides() : ValueToValueMap();
 
-  int Stride = getPtrStride(PSE, Ptr, TheLoop, Strides, true, false);
+  bool CanAddPredicate = !TheLoop->getHeader()->getParent()->hasOptSize();
+  int Stride = getPtrStride(PSE, Ptr, TheLoop, Strides, CanAddPredicate, false);
   if (Stride == 1 || Stride == -1)
     return Stride;
   return 0;

diff --git a/test/Transforms/LoopVectorize/optsize.ll b/test/Transforms/LoopVectorize/optsize.ll
index 403c006eeb57dfbe92b42e253c8c75666a0e325c..1991906494e493ee8ab576ef2fefbd20668d2eaa 100644 (file)
--- a/test/Transforms/LoopVectorize/optsize.ll
+++ b/test/Transforms/LoopVectorize/optsize.ll
@@ -84,6 +84,43 @@ for.end:                                          ; preds = %for.body
   ret i32 0
 }
 
+; PR43371: don't run into an assert due to emitting SCEV runtime checks
+; with OptForSize.
+;
+@cm_array = external global [2592 x i16], align 1
+
+define void @pr43371() optsize {
+;
+; CHECK-LABEL: @pr43371
+; CHECK-NOT:   vector.scevcheck
+;
+; We do not want to generate SCEV predicates when optimising for size, because
+; that will lead to extra code generation such as the SCEV overflow runtime
+; checks. Not generating SCEV predicates can still result in vectorisation as
+; the non-consecutive loads/stores can be scalarized:
+;
+; CHECK: vector.body:
+; CHECK: store i16 0, i16* %{{.*}}, align 1
+; CHECK: store i16 0, i16* %{{.*}}, align 1
+; CHECK: br i1 {{.*}}, label %vector.body
+;
+entry:
+  br label %for.body29
+
+for.cond.cleanup28:
+  unreachable
+
+for.body29:
+  %i24.0170 = phi i16 [ 0, %entry], [ %inc37, %for.body29]
+  %add33 = add i16 undef, %i24.0170
+  %idxprom34 = zext i16 %add33 to i32
+  %arrayidx35 = getelementptr [2592 x i16], [2592 x i16] * @cm_array, i32 0, i32 %idxprom34
+  store i16 0, i16 * %arrayidx35, align 1
+  %inc37 = add i16 %i24.0170, 1
+  %cmp26 = icmp ult i16 %inc37, 756
+  br i1 %cmp26, label %for.body29, label %for.cond.cleanup28
+}
+
 !llvm.module.flags = !{!0}
 !0 = !{i32 1, !"ProfileSummary", !1}
 !1 = !{!2, !3, !4, !5, !6, !7, !8, !9}