[ARM][MVE] canTailPredicateLoop

This implements TTI hook 'preferPredicateOverEpilogue' for MVE.  This is a
first version and it operates on single block loops only. With this change, the
vectoriser will now determine if tail-folding scalar remainder loops is
possible/desired, which is the first step to generate MVE tail-predicated
vector loops.

This is disabled by default for now. I.e,, this is depends on option
-disable-mve-tail-predication, which is off by default.

I will follow up on this soon with a patch for the vectoriser to respect loop
hint 'vectorize.predicate.enable'. I.e., with this loop hint set to Disabled,
we don't want to tail-fold and we shouldn't query this TTI hook, which is
done in D70125.

Differential Revision: https://reviews.llvm.org/D69845

1 files changed, 592 insertions, 27 deletions

diff --git a/llvm/test/Transforms/LoopVectorize/ARM/prefer-tail-loop-folding.ll b/llvm/test/Transforms/LoopVectorize/ARM/prefer-tail-loop-folding.ll
index 9fea4da6e38..d8ada7ae607 100644
--- a/llvm/test/Transforms/LoopVectorize/ARM/prefer-tail-loop-folding.ll
+++ b/llvm/test/Transforms/LoopVectorize/ARM/prefer-tail-loop-folding.ll
@@ -1,33 +1,418 @@
-; RUN: opt -mtriple=thumbv8.1m.main-arm-eabihf < %s -loop-vectorize -S | \
-; RUN:  FileCheck %s -check-prefixes=CHECK,NO-FOLDING
+; RUN: opt -mtriple=thumbv8.1m.main-arm-eabihf \
+; RUN:   -disable-mve-tail-predication=false -loop-vectorize -S < %s | \
+; RUN:   FileCheck %s -check-prefixes=CHECK,NO-FOLDING
 
-; RUN: opt -mtriple=thumbv8.1m.main-arm-eabihf -mattr=-mve < %s -loop-vectorize -enable-arm-maskedldst=true -S | \
-; RUN:  FileCheck %s -check-prefixes=CHECK,NO-FOLDING
+; RUN: opt -mtriple=thumbv8.1m.main-arm-eabihf -mattr=-mve \
+; RUN:   -disable-mve-tail-predication=false -loop-vectorize \
+; RUN:   -enable-arm-maskedldst=true -S < %s | \
+; RUN:   FileCheck %s -check-prefixes=CHECK,NO-FOLDING
 
-; RUN: opt -mtriple=thumbv8.1m.main-arm-eabihf -mattr=+mve < %s -loop-vectorize -enable-arm-maskedldst=false -S | \
-; RUN:  FileCheck %s -check-prefixes=CHECK,NO-FOLDING
+; RUN: opt -mtriple=thumbv8.1m.main-arm-eabihf -mattr=+mve \
+; RUN:   -disable-mve-tail-predication=false -loop-vectorize \
+; RUN:   -enable-arm-maskedldst=false -S < %s | \
+; RUN:   FileCheck %s -check-prefixes=CHECK,NO-FOLDING
+
+; RUN: opt -mtriple=thumbv8.1m.main-arm-eabihf -mattr=+mve \
+; RUN:   -disable-mve-tail-predication=true -loop-vectorize \
+; RUN:   -enable-arm-maskedldst=true -S < %s | \
+; RUN:   FileCheck %s -check-prefixes=CHECK,NO-FOLDING
 
 ; Disabling the low-overhead branch extension will make
 ; 'isHardwareLoopProfitable' return false, so that we test avoiding folding for
 ; these cases.
-; RUN: opt -mtriple=thumbv8.1m.main-arm-eabihf -mattr=+mve,-lob < %s -loop-vectorize -enable-arm-maskedldst=true -S | \
-; RUN:  FileCheck %s -check-prefixes=CHECK,NO-FOLDING
+; RUN: opt -mtriple=thumbv8.1m.main-arm-eabihf -mattr=+mve,-lob \
+; RUN:   -disable-mve-tail-predication=false -loop-vectorize \
+; RUN:   -enable-arm-maskedldst=true -S < %s | \
+; RUN:   FileCheck %s -check-prefixes=CHECK,NO-FOLDING
 
-; RUN: opt -mtriple=thumbv8.1m.main-arm-eabihf -mattr=+mve < %s -loop-vectorize -enable-arm-maskedldst=true -S | \
-; RUN:  FileCheck %s -check-prefixes=CHECK,PREFER-FOLDING
+; RUN: opt -mtriple=thumbv8.1m.main-arm-eabihf -mattr=+mve.fp \
+; RUN:   -disable-mve-tail-predication=false -loop-vectorize \
+; RUN:   -enable-arm-maskedldst=true -S < %s | \
+; RUN:   FileCheck %s -check-prefixes=CHECK,PREFER-FOLDING
 
-define dso_local void @tail_folding(i32* noalias nocapture %A, i32* noalias nocapture readonly %B, i32* noalias nocapture readonly %C) {
-; CHECK-LABEL: tail_folding(
-;
-; NO-FOLDING-NOT:  call <4 x i32> @llvm.masked.load.v4i32.p0v4i32(
-; NO-FOLDING-NOT:  call void @llvm.masked.store.v4i32.p0v4i32(
+define void @prefer_folding(i32* noalias nocapture %A, i32* noalias nocapture readonly %B, i32* noalias nocapture readonly %C) #0 {
+; CHECK-LABEL:    prefer_folding(
+; PREFER-FOLDING: vector.body:
+; PREFER-FOLDING: call <4 x i32> @llvm.masked.load.v4i32.p0v4i32
+; PREFER-FOLDING: call <4 x i32> @llvm.masked.load.v4i32.p0v4i32
+; PREFER-FOLDING: call void @llvm.masked.store.v4i32.p0v4i32
+; PREFER-FOLDING: br i1 %{{.*}}, label %{{.*}}, label %vector.body
 ;
-; TODO: this needs implementation of TTI::preferPredicateOverEpilogue,
-; then this will be tail-folded too:
+; NO-FOLDING-NOT: call <4 x i32> @llvm.masked.load.v4i32.p0v4i32(
+; NO-FOLDING-NOT: call void @llvm.masked.store.v4i32.p0v4i32(
+; NO-FOLDING:     br i1 %{{.*}}, label %{{.*}}, label %for.body
+entry:
+  br label %for.body
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %i.09 = phi i32 [ 0, %entry ], [ %add3, %for.body ]
+  %arrayidx = getelementptr inbounds i32, i32* %B, i32 %i.09
+  %0 = load i32, i32* %arrayidx, align 4
+  %arrayidx1 = getelementptr inbounds i32, i32* %C, i32 %i.09
+  %1 = load i32, i32* %arrayidx1, align 4
+  %add = add nsw i32 %1, %0
+  %arrayidx2 = getelementptr inbounds i32, i32* %A, i32 %i.09
+  store i32 %add, i32* %arrayidx2, align 4
+  %add3 = add nuw nsw i32 %i.09, 1
+  %exitcond = icmp eq i32 %add3, 431
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body
+}
+
+define void @mixed_types(i16* noalias nocapture %A, i16* noalias nocapture readonly %B, i16* noalias nocapture readonly %C, i32* noalias nocapture %D, i32* noalias nocapture readonly %E, i32* noalias nocapture readonly %F) #0 {
+; CHECK-LABEL:        mixed_types(
+; PREFER-FOLDING:     vector.body:
+; PREFER-FOLDING:     call <4 x i16> @llvm.masked.load.v4i16.p0v4i16
+; PREFER-FOLDING:     call <4 x i16> @llvm.masked.load.v4i16.p0v4i16
+; PREFER-FOLDING:     call void @llvm.masked.store.v4i16.p0v4i16
+; PREFER-FOLDING:     call <4 x i32> @llvm.masked.load.v4i32.p0v4i32
+; PREFER-FOLDING:     call <4 x i32> @llvm.masked.load.v4i32.p0v4i32
+; PREFER-FOLDING:     call void @llvm.masked.store.v4i32.p0v4i32
+; PREFER-FOLDING:     br i1 %{{.*}}, label %{{.*}}, label %vector.body
+entry:
+  br label %for.body
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %i.018 = phi i32 [ 0, %entry ], [ %add9, %for.body ]
+  %arrayidx = getelementptr inbounds i16, i16* %B, i32 %i.018
+  %0 = load i16, i16* %arrayidx, align 2
+  %arrayidx1 = getelementptr inbounds i16, i16* %C, i32 %i.018
+  %1 = load i16, i16* %arrayidx1, align 2
+  %add = add i16 %1, %0
+  %arrayidx4 = getelementptr inbounds i16, i16* %A, i32 %i.018
+  store i16 %add, i16* %arrayidx4, align 2
+  %arrayidx5 = getelementptr inbounds i32, i32* %E, i32 %i.018
+  %2 = load i32, i32* %arrayidx5, align 4
+  %arrayidx6 = getelementptr inbounds i32, i32* %F, i32 %i.018
+  %3 = load i32, i32* %arrayidx6, align 4
+  %add7 = add nsw i32 %3, %2
+  %arrayidx8 = getelementptr inbounds i32, i32* %D, i32 %i.018
+  store i32 %add7, i32* %arrayidx8, align 4
+  %add9 = add nuw nsw i32 %i.018, 1
+  %exitcond = icmp eq i32 %add9, 431
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body
+}
+
+define void @unsupported_i64_type(i64* noalias nocapture %A, i64* noalias nocapture readonly %B, i64* noalias nocapture readonly %C) #0 {
+; CHECK-LABEL:        unsupported_i64_type(
+; PREFER-FOLDING-NOT: vector.body:
+; PREFER-FOLDING-NOT: llvm.masked.load
+; PREFER-FOLDING-NOT: llvm.masked.store
+; PREFER-FOLDING:     for.body:
+entry:
+  br label %for.body
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %i.09 = phi i32 [ 0, %entry ], [ %add3, %for.body ]
+  %arrayidx = getelementptr inbounds i64, i64* %B, i32 %i.09
+  %0 = load i64, i64* %arrayidx, align 8
+  %arrayidx1 = getelementptr inbounds i64, i64* %C, i32 %i.09
+  %1 = load i64, i64* %arrayidx1, align 8
+  %add = add nsw i64 %1, %0
+  %arrayidx2 = getelementptr inbounds i64, i64* %A, i32 %i.09
+  store i64 %add, i64* %arrayidx2, align 8
+  %add3 = add nuw nsw i32 %i.09, 1
+  %exitcond = icmp eq i32 %add3, 431
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body
+}
+
+define void @zero_extending_load_allowed(i32* noalias nocapture %A, i8* noalias nocapture readonly %B, i32* noalias nocapture readonly %C) #0 {
+; CHECK-LABEL:    zero_extending_load_allowed(
+; PREFER-FOLDING: vector.body:
+; PREFER-FOLDING: call <4 x i8> @llvm.masked.load.v4i8.p0v4i8
+; PREFER-FOLDING: call <4 x i32> @llvm.masked.load.v4i32.p0v4i32
+; PREFER-FOLDING: call void @llvm.masked.store.v4i32.p0v4i32
+; PREFER-FOLDING: br i1 %{{.*}}, label %{{.*}}, label %vector.body
+entry:
+  br label %for.body
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %i.09 = phi i32 [ 0, %entry ], [ %add3, %for.body ]
+  %arrayidx = getelementptr inbounds i8, i8* %B, i32 %i.09
+  %0 = load i8, i8* %arrayidx, align 1
+  %conv = zext i8 %0 to i32
+  %arrayidx1 = getelementptr inbounds i32, i32* %C, i32 %i.09
+  %1 = load i32, i32* %arrayidx1, align 4
+  %add = add nsw i32 %1, %conv
+  %arrayidx2 = getelementptr inbounds i32, i32* %A, i32 %i.09
+  store i32 %add, i32* %arrayidx2, align 4
+  %add3 = add nuw nsw i32 %i.09, 1
+  %exitcond = icmp eq i32 %add3, 431
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body
+}
+
+define void @sign_extending_load_allowed(i32* noalias nocapture %A, i8* noalias nocapture readonly %B, i32* noalias nocapture readonly %C) #0 {
+; CHECK-LABEL:    sign_extending_load_allowed(
+; PREFER-FOLDING: vector.body:
+; PREFER-FOLDING: call <4 x i8> @llvm.masked.load.v4i8.p0v4i8
+; PREFER-FOLDING: call <4 x i32> @llvm.masked.load.v4i32.p0v4i32
+; PREFER-FOLDING: call void @llvm.masked.store.v4i32.p0v4i32
+; PREFER-FOLDING: br i1 %{{.*}}, label %{{.*}}, label %vector.body
+entry:
+  br label %for.body
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %i.09 = phi i32 [ 0, %entry ], [ %add3, %for.body ]
+  %arrayidx = getelementptr inbounds i8, i8* %B, i32 %i.09
+  %0 = load i8, i8* %arrayidx, align 1
+  %conv = sext i8 %0 to i32
+  %arrayidx1 = getelementptr inbounds i32, i32* %C, i32 %i.09
+  %1 = load i32, i32* %arrayidx1, align 4
+  %add = add nsw i32 %1, %conv
+  %arrayidx2 = getelementptr inbounds i32, i32* %A, i32 %i.09
+  store i32 %add, i32* %arrayidx2, align 4
+  %add3 = add nuw nsw i32 %i.09, 1
+  %exitcond = icmp eq i32 %add3, 431
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body
+}
+
+define void @narrowing_load_not_allowed(i8* noalias nocapture %A, i8* noalias nocapture readonly %B, i16* noalias nocapture readonly %C) #0 {
+; CHECK-LABEL:        narrowing_load_not_allowed(
+; PREFER-FOLDING:     vector.body:
+; PREFER-FOLDING-NOT: llvm.masked.load
+; PREFER-FOLDING-NOT: llvm.masked.store
+; PREFER-FOLDING:     br i1 %{{.*}}, label %{{.*}}, label %vector.body
+entry:
+  br label %for.body
+
+for.cond.cleanup:                                 ; preds = %for.body
+  ret void
+
+for.body:                                         ; preds = %for.body, %entry
+  %i.012 = phi i32 [ 0, %entry ], [ %add6, %for.body ]
+  %arrayidx = getelementptr inbounds i16, i16* %C, i32 %i.012
+  %0 = load i16, i16* %arrayidx, align 2
+  %arrayidx1 = getelementptr inbounds i8, i8* %B, i32 %i.012
+  %1 = load i8, i8* %arrayidx1, align 1
+  %conv3 = trunc i16 %0 to i8
+  %add = add i8 %1, %conv3
+  %arrayidx5 = getelementptr inbounds i8, i8* %A, i32 %i.012
+  store i8 %add, i8* %arrayidx5, align 1
+  %add6 = add nuw nsw i32 %i.012, 1
+  %exitcond = icmp eq i32 %add6, 431
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body
+}
+
+define void @narrowing_store_allowed(i8* noalias nocapture %A, i32* noalias nocapture readonly %B, i32* noalias nocapture readonly %C) #0 {
+; CHECK-LABEL:    narrowing_store_allowed(
+; PREFER-FOLDING: call void @llvm.masked.store.v4i8.p0v4i8
+; PREFER-FOLDING: br i1 %{{.*}}, label %{{.*}}, label %vector.body
+entry:
+  br label %for.body
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %i.09 = phi i32 [ 0, %entry ], [ %add3, %for.body ]
+  %arrayidx = getelementptr inbounds i32, i32* %B, i32 %i.09
+  %0 = load i32, i32* %arrayidx, align 4
+  %arrayidx1 = getelementptr inbounds i32, i32* %C, i32 %i.09
+  %1 = load i32, i32* %arrayidx1, align 4
+  %add = add nsw i32 %1, %0
+  %conv = trunc i32 %add to i8
+  %arrayidx2 = getelementptr inbounds i8, i8* %A, i32 %i.09
+  store i8 %conv, i8* %arrayidx2, align 1
+  %add3 = add nuw nsw i32 %i.09, 1
+  %exitcond = icmp eq i32 %add3, 431
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body
+}
+
+; This is a trunc not connected to a store, so we don't allow this.
+; TODO: this is conservative, because the trunc is only used in the
+; loop control statements, and thus not affecting element sizes, so
+; we could allow this case.
+define void @trunc_not_allowed(i32* noalias nocapture %A, i32* noalias nocapture readonly %B, i32* noalias nocapture readonly %C) #0 {
+; CHECK-LABEL:        trunc_not_allowed(
+; PREFER-FOLDING:     vector.body:
+; PREFER-FOLDING-NOT: llvm.masked.load
+; PREFER-FOLDING-NOT: llvm.masked.store
+; PREFER-FOLDING:     br i1 %{{.*}}, label %{{.*}}, label %vector.body
+entry:
+  br label %for.body
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %i.09 = phi i32 [ 0, %entry ], [ %add3, %for.body ]
+  %arrayidx = getelementptr inbounds i32, i32* %B, i32 %i.09
+  %0 = load i32, i32* %arrayidx, align 4
+  %arrayidx1 = getelementptr inbounds i32, i32* %C, i32 %i.09
+  %1 = load i32, i32* %arrayidx1, align 4
+  %add = add nsw i32 %1, %0
+  %arrayidx2 = getelementptr inbounds i32, i32* %A, i32 %i.09
+  store i32 %add, i32* %arrayidx2, align 4
+  %add3 = add nuw nsw i32 %i.09, 1
+
+  %add.iv = trunc i32 %add3 to i16
+
+  %exitcond = icmp eq i16 %add.iv, 431
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body
+}
+
+define void @trunc_not_allowed_different_vec_elemns(i32* noalias nocapture %A, i32* noalias nocapture readonly %B, i32* noalias nocapture readonly %C, i16* noalias nocapture %D) #0 {
+; CHECK-LABEL:        trunc_not_allowed_different_vec_elemns(
+; PREFER-FOLDING:     vector.body:
+; PREFER-FOLDING-NOT: llvm.masked.load
+; PREFER-FOLDING-NOT: llvm.masked.store
+; PREFER-FOLDING:     br i1 %{{.*}}, label %{{.*}}, label %vector.body
+entry:
+  br label %for.body
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %i.021 = phi i32 [ 0, %entry ], [ %add9, %for.body ]
+  %arrayidx = getelementptr inbounds i32, i32* %B, i32 %i.021
+  %0 = load i32, i32* %arrayidx, align 4
+  %arrayidx1 = getelementptr inbounds i32, i32* %C, i32 %i.021
+  %1 = load i32, i32* %arrayidx1, align 4
+  %add = add nsw i32 %1, %0
+  %arrayidx2 = getelementptr inbounds i32, i32* %A, i32 %i.021
+  store i32 %add, i32* %arrayidx2, align 4
+  %add.tr = trunc i32 %add to i16
+  %conv7 = shl i16 %add.tr, 1
+  %arrayidx8 = getelementptr inbounds i16, i16* %D, i32 %i.021
+  store i16 %conv7, i16* %arrayidx8, align 2
+  %add9 = add nuw nsw i32 %i.021, 1
+  %exitcond = icmp eq i32 %add9, 431
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body
+}
+
+
+@tab = common global [32 x i8] zeroinitializer, align 1
+
+define i32 @icmp_not_allowed() #0 {
+; CHECK-LABEL:        icmp_not_allowed(
+; PREFER-FOLDING:     vector.body:
+; PREFER-FOLDING-NOT: llvm.masked.load
+; PREFER-FOLDING-NOT: llvm.masked.store
+; PREFER-FOLDING:     br i1 %{{.*}}, label %{{.*}}, label %vector.body
+entry:
+  br label %for.body
+
+for.body:
+  %i.08 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
+  %arrayidx = getelementptr inbounds [32 x i8], [32 x i8]* @tab, i32 0, i32 %i.08
+  %0 = load i8, i8* %arrayidx, align 1
+  %cmp1 = icmp eq i8 %0, 0
+  %. = select i1 %cmp1, i8 2, i8 1
+  store i8 %., i8* %arrayidx, align 1
+  %inc = add nsw i32 %i.08, 1
+  %exitcond = icmp slt i32 %inc, 1000
+  br i1 %exitcond, label %for.body, label %for.end
+
+for.end:
+  ret i32 0
+}
+
+define void @pragma_vect_predicate_disable(i32* noalias nocapture %A, i32* noalias nocapture readonly %B, i32* noalias nocapture readonly %C) #0 {
+; CHECK-LABEL: pragma_vect_predicate_disable(
 ;
-; PREFER-FOLDING-NOT:  call <4 x i32> @llvm.masked.load.v4i32.p0v4i32(
-; PREFER-FOLDING-NOT:  call void @llvm.masked.store.v4i32.p0v4i32(
+; FIXME:
+; respect loop hint predicate.enable = false, and don't tail-fold here:
 ;
+; PREFER-FOLDING: call <4 x i32> @llvm.masked.load.v4i32.p0v4i32
+; PREFER-FOLDING: call <4 x i32> @llvm.masked.load.v4i32.p0v4i32
+; PREFER-FOLDING: call void @llvm.masked.store.v4i32.p0v4i32
+; PREFER-FOLDING: br i1 %{{.*}}, label %{{.*}}, label %vector.body
+entry:
+  br label %for.body
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %i.09 = phi i32 [ 0, %entry ], [ %add3, %for.body ]
+  %arrayidx = getelementptr inbounds i32, i32* %B, i32 %i.09
+  %0 = load i32, i32* %arrayidx, align 4
+  %arrayidx1 = getelementptr inbounds i32, i32* %C, i32 %i.09
+  %1 = load i32, i32* %arrayidx1, align 4
+  %add = add nsw i32 %1, %0
+  %arrayidx2 = getelementptr inbounds i32, i32* %A, i32 %i.09
+  store i32 %add, i32* %arrayidx2, align 4
+  %add3 = add nuw nsw i32 %i.09, 1
+  %exitcond = icmp eq i32 %add3, 431
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body, !llvm.loop !7
+}
+
+; Test directions for array indices i and N-1. I.e. check strides 1 and -1, and
+; force vectorisation with a loop hint.
+define void @strides_different_direction(i32* noalias nocapture %A, i32* noalias nocapture readonly %B, i32* noalias nocapture readonly %C, i32 %N) #0 {
+; CHECK-LABEL: strides_different_direction(
+; PREFER-FOLDING:     vector.body:
+; PREFER-FOLDING-NOT: llvm.masked.load
+; PREFER-FOLDING-NOT: llvm.masked.store
+; PREFER-FOLDING:     br i1 %{{.*}}, label %{{.*}}, label %vector.body
+entry:
+  br label %for.body
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %i.09 = phi i32 [ 0, %entry ], [ %add3, %for.body ]
+  %arrayidx = getelementptr inbounds i32, i32* %B, i32 %i.09
+  %0 = load i32, i32* %arrayidx, align 4
+  %sub = sub nsw i32 %N, %i.09
+  %arrayidx1 = getelementptr inbounds i32, i32* %C, i32 %sub
+  %1 = load i32, i32* %arrayidx1, align 4
+  %add = add nsw i32 %1, %0
+  %arrayidx2 = getelementptr inbounds i32, i32* %A, i32 %i.09
+  store i32 %add, i32* %arrayidx2, align 4
+  %add3 = add nuw nsw i32 %i.09, 1
+  %exitcond = icmp eq i32 %add3, 431
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body, !llvm.loop !10
+}
+
+define void @stride_4(i32* noalias nocapture %A, i32* noalias nocapture readonly %B, i32* noalias nocapture readonly %C) #0 {
+; CHECK-LABEL:        stride_4(
+; PREFER-FOLDING:     vector.body:
+; PREFER-FOLDING-NOT: llvm.masked.load
+; PREFER-FOLDING-NOT: llvm.masked.store
+; PREFER-FOLDING:     br i1 %{{.*}}, label %{{.*}}, label %vector.body
+entry:
+  br label %for.body
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %i.09 = phi i32 [ 0, %entry ], [ %add3, %for.body ]
+  %arrayidx = getelementptr inbounds i32, i32* %B, i32 %i.09
+  %0 = load i32, i32* %arrayidx, align 4
+  %arrayidx1 = getelementptr inbounds i32, i32* %C, i32 %i.09
+  %1 = load i32, i32* %arrayidx1, align 4
+  %add = add nsw i32 %1, %0
+  %arrayidx2 = getelementptr inbounds i32, i32* %A, i32 %i.09
+  store i32 %add, i32* %arrayidx2, align 4
+  %add3 = add nuw nsw i32 %i.09, 4
+  %cmp = icmp ult i32 %add3, 731
+  br i1 %cmp, label %for.body, label %for.cond.cleanup, !llvm.loop !5
+}
+
+define void @too_many_loop_blocks(i32* noalias nocapture %A, i32* noalias nocapture readonly %B, i32* noalias nocapture readonly %C) #0 {
+; CHECK-LABEL:        too_many_loop_blocks(
+; PREFER-FOLDING:     vector.body:
+; PREFER-FOLDING-NOT: llvm.masked.load
+; PREFER-FOLDING-NOT: llvm.masked.store
+; PREFER-FOLDING:     br i1 %{{.*}}, label %{{.*}}, label %vector.body
 entry:
   br label %for.body
 
@@ -35,15 +420,195 @@ for.cond.cleanup:
   ret void
 
 for.body:
-  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
-  %arrayidx = getelementptr inbounds i32, i32* %B, i64 %indvars.iv
+  %i.09 = phi i32 [ 0, %entry ], [ %add3, %loopincr ]
+  %arrayidx = getelementptr inbounds i32, i32* %B, i32 %i.09
   %0 = load i32, i32* %arrayidx, align 4
-  %arrayidx2 = getelementptr inbounds i32, i32* %C, i64 %indvars.iv
-  %1 = load i32, i32* %arrayidx2, align 4
+  %arrayidx1 = getelementptr inbounds i32, i32* %C, i32 %i.09
+  %1 = load i32, i32* %arrayidx1, align 4
   %add = add nsw i32 %1, %0
-  %arrayidx4 = getelementptr inbounds i32, i32* %A, i64 %indvars.iv
-  store i32 %add, i32* %arrayidx4, align 4
-  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
-  %exitcond = icmp eq i64 %indvars.iv.next, 430
+  %arrayidx2 = getelementptr inbounds i32, i32* %A, i32 %i.09
+  store i32 %add, i32* %arrayidx2, align 4
+  br label %loopincr
+
+loopincr:
+  %add3 = add nuw nsw i32 %i.09, 1
+  %exitcond = icmp eq i32 %add3, 431
   br i1 %exitcond, label %for.cond.cleanup, label %for.body
 }
+
+define dso_local void @half(half* noalias nocapture %A, half* noalias nocapture readonly %B, half* noalias nocapture readonly %C) #0 {
+; CHECK-LABEL:    half(
+; PREFER-FOLDING: vector.body:
+; PREFER-FOLDING: call <8 x half> @llvm.masked.load.v8f16.p0v8f16
+; PREFER-FOLDING: call <8 x half> @llvm.masked.load.v8f16.p0v8f16
+; PREFER-FOLDING: call void @llvm.masked.store.v8f16.p0v8f16
+; PREFER-FOLDING: br i1 %{{.*}}, label %{{.*}}, label %vector.body
+entry:
+  br label %for.body
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %i.09 = phi i32 [ 0, %entry ], [ %add3, %for.body ]
+  %arrayidx = getelementptr inbounds half, half* %B, i32 %i.09
+  %0 = load half, half* %arrayidx, align 2
+  %arrayidx1 = getelementptr inbounds half, half* %C, i32 %i.09
+  %1 = load half, half* %arrayidx1, align 2
+  %add = fadd fast half %1, %0
+  %arrayidx2 = getelementptr inbounds half, half* %A, i32 %i.09
+  store half %add, half* %arrayidx2, align 2
+  %add3 = add nuw nsw i32 %i.09, 1
+  %exitcond = icmp eq i32 %add3, 431
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body
+}
+
+define void @float(float* noalias nocapture %A, float* noalias nocapture readonly %B, float* noalias nocapture readonly %C) #0 {
+; CHECK-LABEL:    float(
+; PREFER-FOLDING: vector.body:
+; PREFER-FOLDING: call <4 x float> @llvm.masked.load.v4f32.p0v4f32
+; PREFER-FOLDING: call <4 x float> @llvm.masked.load.v4f32.p0v4f32
+; PREFER-FOLDING: call void @llvm.masked.store.v4f32.p0v4f32
+; PREFER-FOLDING: br i1 %{{.*}}, label %{{.*}}, label %vector.body
+entry:
+  br label %for.body
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %i.09 = phi i32 [ 0, %entry ], [ %add3, %for.body ]
+  %arrayidx = getelementptr inbounds float, float* %B, i32 %i.09
+  %0 = load float, float* %arrayidx, align 4
+  %arrayidx1 = getelementptr inbounds float, float* %C, i32 %i.09
+  %1 = load float, float* %arrayidx1, align 4
+  %add = fadd fast float %1, %0
+  %arrayidx2 = getelementptr inbounds float, float* %A, i32 %i.09
+  store float %add, float* %arrayidx2, align 4
+  %add3 = add nuw nsw i32 %i.09, 1
+  %exitcond = icmp eq i32 %add3, 431
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body, !llvm.loop !10
+}
+
+define void @double(double* noalias nocapture %A, double* noalias nocapture readonly %B, double* noalias nocapture readonly %C) #0 {
+; CHECK-LABEL:        double(
+; PREFER-FOLDING:     for.body:
+; PREFER-FOLDING-NOT: vector.body:
+entry:
+  br label %for.body
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %i.09 = phi i32 [ 0, %entry ], [ %add3, %for.body ]
+  %arrayidx = getelementptr inbounds double, double* %B, i32 %i.09
+  %0 = load double, double* %arrayidx, align 8
+  %arrayidx1 = getelementptr inbounds double, double* %C, i32 %i.09
+  %1 = load double, double* %arrayidx1, align 8
+  %add = fadd fast double %1, %0
+  %arrayidx2 = getelementptr inbounds double, double* %A, i32 %i.09
+  store double %add, double* %arrayidx2, align 8
+  %add3 = add nuw nsw i32 %i.09, 1
+  %exitcond = icmp eq i32 %add3, 431
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body
+}
+
+; TODO: this fpext could be allowed, but we don't lower it very efficiently yet,
+; so reject this for now.
+define void @fpext_allowed(float* noalias nocapture %A, half* noalias nocapture readonly %B, float* noalias nocapture readonly %C) #0 {
+; CHECK-LABEL:        fpext_allowed(
+; PREFER-FOLDING:     vector.body:
+; PREFER-FOLDING-NOT: llvm.masked.load
+; PREFER-FOLDING-NOT: llvm.masked.store
+; PREFER-FOLDING:     br i1 %{{.*}}, label %{{.*}}, label %vector.body
+entry:
+  br label %for.body
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %i.09 = phi i32 [ 0, %entry ], [ %add3, %for.body ]
+  %arrayidx = getelementptr inbounds half, half* %B, i32 %i.09
+  %0 = load half, half* %arrayidx, align 2
+  %conv = fpext half %0 to float
+  %arrayidx1 = getelementptr inbounds float, float* %C, i32 %i.09
+  %1 = load float, float* %arrayidx1, align 4
+  %add = fadd fast float %1, %conv
+  %arrayidx2 = getelementptr inbounds float, float* %A, i32 %i.09
+  store float %add, float* %arrayidx2, align 4
+  %add3 = add nuw nsw i32 %i.09, 1
+  %exitcond = icmp eq i32 %add3, 431
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body
+}
+
+; TODO: this fptrunc could be allowed, but we don't lower it very efficiently yet,
+; so reject this for now.
+define void @fptrunc_allowed(half* noalias nocapture %A, float* noalias nocapture readonly %B, float* noalias nocapture readonly %C) #0 {
+; CHECK-LABEL:        fptrunc_allowed(
+; PREFER-FOLDING:     vector.body:
+; PREFER-FOLDING-NOT: llvm.masked.load
+; PREFER-FOLDING-NOT: llvm.masked.store
+; PREFER-FOLDING:     br i1 %{{.*}}, label %{{.*}}, label %vector.body
+entry:
+  br label %for.body
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %i.09 = phi i32 [ 0, %entry ], [ %add3, %for.body ]
+  %arrayidx = getelementptr inbounds float, float* %B, i32 %i.09
+  %0 = load float, float* %arrayidx, align 4
+  %arrayidx1 = getelementptr inbounds float, float* %C, i32 %i.09
+  %1 = load float, float* %arrayidx1, align 4
+  %add = fadd fast float %1, %0
+  %conv = fptrunc float %add to half
+  %arrayidx2 = getelementptr inbounds half, half* %A, i32 %i.09
+  store half %conv, half* %arrayidx2, align 2
+  %add3 = add nuw nsw i32 %i.09, 1
+  %exitcond = icmp eq i32 %add3, 431
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body
+}
+
+define void @fptrunc_not_allowed(float* noalias nocapture %A, float* noalias nocapture readonly %B, float* noalias nocapture readonly %C, half* noalias nocapture %D) #0 {
+; CHECK-LABEL:        fptrunc_not_allowed(
+; PREFER-FOLDING:     vector.body:
+; PREFER-FOLDING-NOT: llvm.masked.load
+; PREFER-FOLDING-NOT: llvm.masked.store
+; PREFER-FOLDING:     br i1 %{{.*}}, label %{{.*}}, label %vector.body
+entry:
+  br label %for.body
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %i.017 = phi i32 [ 0, %entry ], [ %add6, %for.body ]
+  %arrayidx = getelementptr inbounds float, float* %B, i32 %i.017
+  %0 = load float, float* %arrayidx, align 4
+  %arrayidx1 = getelementptr inbounds float, float* %C, i32 %i.017
+  %1 = load float, float* %arrayidx1, align 4
+  %add = fadd fast float %1, %0
+  %arrayidx2 = getelementptr inbounds float, float* %A, i32 %i.017
+  store float %add, float* %arrayidx2, align 4
+  %conv = fptrunc float %add to half
+  %factor = fmul fast half %conv, 0xH4000
+  %arrayidx5 = getelementptr inbounds half, half* %D, i32 %i.017
+  store half %factor, half* %arrayidx5, align 2
+  %add6 = add nuw nsw i32 %i.017, 1
+  %exitcond = icmp eq i32 %add6, 431
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body
+}
+
+attributes #0 = { nofree norecurse nounwind "target-features"="+armv8.1-m.main,+mve.fp" }
+
+!5 = distinct !{!5, !6}
+!6 = !{!"llvm.loop.vectorize.enable", i1 true}
+
+!7 = distinct !{!7, !8}
+!8 = !{!"llvm.loop.vectorize.predicate.enable", i1 false}
+
+!10 = distinct !{!10, !11}
+!11 = !{!"llvm.loop.vectorize.width", i32 4}