[LV] Avoid vectorizing loops under opt for size that involve SCEV checks

Fix PR39417, PR39497

The loop vectorizer may generate runtime SCEV checks for overflow and stride==1
cases, leading to execution of original scalar loop. The latter is forbidden
when optimizing for size. An assert introduced in r344743 triggered the above
PR's showing it does happen. This patch fixes this behavior by preventing
vectorization in such cases.

Differential Revision: https://reviews.llvm.org/D53612

llvm-svn: 345959

2 files changed, 114 insertions, 0 deletions

diff --git a/llvm/test/Transforms/LoopVectorize/X86/optsize.ll b/llvm/test/Transforms/LoopVectorize/X86/optsize.ll
index 508823475ea..9fa65534f32 100644
--- a/llvm/test/Transforms/LoopVectorize/X86/optsize.ll
+++ b/llvm/test/Transforms/LoopVectorize/X86/optsize.ll
@@ -3,6 +3,7 @@
 ; will produce a tail loop with the optimize for size or the minimize size
 ; attributes. This is a target-dependent version of the test.
 ; RUN: opt < %s -loop-vectorize -force-vector-width=64 -S -mtriple=x86_64-unknown-linux -mcpu=skx | FileCheck %s
+; RUN: opt < %s -loop-vectorize -S -mtriple=x86_64-unknown-linux -mcpu=skx | FileCheck %s --check-prefix AUTOVF
 
 target datalayout = "E-m:e-p:32:32-i64:32-f64:32:64-a:0:32-n32-S128"
 
@@ -136,3 +137,62 @@ for.end:                                          ; preds = %for.body
 
 attributes #1 = { minsize }
 
+
+; We can't vectorize this one because we version for stride==1; even having TC
+; a multiple of VF.
+; CHECK-LABEL: @scev4stride1
+; CHECK-NOT: vector.scevcheck
+; CHECK-NOT: vector.body:
+; CHECK-LABEL: for.body:
+; AUTOVF-LABEL: @scev4stride1
+; AUTOVF-NOT: vector.scevcheck
+; AUTOVF-NOT: vector.body:
+; AUTOVF-LABEL: for.body:
+define void @scev4stride1(i32* noalias nocapture %a, i32* noalias nocapture readonly %b, i32 %k) #2 {
+for.body.preheader:
+  br label %for.body
+
+for.body:                                         ; preds = %for.body.preheader, %for.body
+  %i.07 = phi i32 [ %inc, %for.body ], [ 0, %for.body.preheader ]
+  %mul = mul nsw i32 %i.07, %k
+  %arrayidx = getelementptr inbounds i32, i32* %b, i32 %mul
+  %0 = load i32, i32* %arrayidx, align 4
+  %arrayidx1 = getelementptr inbounds i32, i32* %a, i32 %i.07
+  store i32 %0, i32* %arrayidx1, align 4
+  %inc = add nuw nsw i32 %i.07, 1
+  %exitcond = icmp eq i32 %inc, 256
+  br i1 %exitcond, label %for.end.loopexit, label %for.body
+
+for.end.loopexit:                                 ; preds = %for.body
+  ret void
+}
+
+attributes #2 = { optsize }
+
+
+; PR39497
+; We can't vectorize this one because we version for overflow check and tiny
+; trip count leads to opt-for-size (which otherwise could fold the tail by
+; masking).
+; CHECK-LABEL: @main
+; CHECK-NOT: vector.scevcheck
+; CHECK-NOT: vector.body:
+; CHECK-LABEL: for.cond:
+; AUTOVF-LABEL: @main
+; AUTOVF-NOT: vector.scevcheck
+; AUTOVF-NOT: vector.body:
+; AUTOVF-LABEL: for.cond:
+define i32 @main() local_unnamed_addr {
+while.cond:
+  br label %for.cond
+
+for.cond:
+  %d.0 = phi i32 [ 0, %while.cond ], [ %add, %for.cond ]
+  %conv = and i32 %d.0, 65535
+  %cmp = icmp ult i32 %conv, 4
+  %add = add nuw nsw i32 %conv, 1
+  br i1 %cmp, label %for.cond, label %while.cond.loopexit
+
+while.cond.loopexit:
+  ret i32 0
+}
diff --git a/llvm/test/Transforms/LoopVectorize/pr39417-optsize-scevchecks.ll b/llvm/test/Transforms/LoopVectorize/pr39417-optsize-scevchecks.ll
new file mode 100644
index 00000000000..6032fb18a38
--- /dev/null
+++ b/llvm/test/Transforms/LoopVectorize/pr39417-optsize-scevchecks.ll
@@ -0,0 +1,54 @@
+; RUN: opt -S -loop-vectorize -force-vector-width=4 -force-vector-interleave=1 < %s | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+; PR39417
+; Check that the need for overflow check prevents vectorizing a loop with tiny
+; trip count (which implies opt for size).
+; CHECK-LABEL: @func_34
+; CHECK-NOT: vector.scevcheck
+; CHECK-NOT: vector.body:
+; CHECK-LABEL: bb67:
+define void @func_34() {
+bb1:
+  br label %bb67
+
+bb67:
+  %storemerge2 = phi i32 [ 0, %bb1 ], [ %_tmp2300, %bb67 ]
+  %sext = shl i32 %storemerge2, 16
+  %_tmp2299 = ashr exact i32 %sext, 16
+  %_tmp2300 = add nsw i32 %_tmp2299, 1
+  %_tmp2310 = trunc i32 %_tmp2300 to i16
+  %_tmp2312 = icmp slt i16 %_tmp2310, 3
+  br i1 %_tmp2312, label %bb67, label %bb68
+
+bb68:
+  ret void
+}
+
+; Check that the need for stride==1 check prevents vectorizing a loop under opt
+; for size.
+; CHECK-LABEL: @scev4stride1
+; CHECK-NOT: vector.scevcheck
+; CHECK-NOT: vector.body:
+; CHECK-LABEL: for.body:
+define void @scev4stride1(i32* noalias nocapture %a, i32* noalias nocapture readonly %b, i32 %k) #0 {
+for.body.preheader:
+  br label %for.body
+
+for.body:
+  %i.07 = phi i32 [ %inc, %for.body ], [ 0, %for.body.preheader ]
+  %mul = mul nsw i32 %i.07, %k
+  %arrayidx = getelementptr inbounds i32, i32* %b, i32 %mul
+  %0 = load i32, i32* %arrayidx, align 4
+  %arrayidx1 = getelementptr inbounds i32, i32* %a, i32 %i.07
+  store i32 %0, i32* %arrayidx1, align 4
+  %inc = add nuw nsw i32 %i.07, 1
+  %exitcond = icmp eq i32 %inc, 1024
+  br i1 %exitcond, label %for.end.loopexit, label %for.body
+
+for.end.loopexit:
+  ret void
+}
+
+attributes #0 = { optsize }