[llvm-bugs] [Bug 37248] New: LoopVectorizer triggers "Instruction does not dominate all uses!" after r326079

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=37248

            Bug ID: 37248
           Summary: LoopVectorizer triggers "Instruction does not dominate
                    all uses!" after r326079
           Product: new-bugs
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: mikael.holmen at ericsson.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 20226
  --> https://bugs.llvm.org/attachment.cgi?id=20226&action=edit
reproducer

Running

 opt -loop-vectorize -S -o - tr15930.ll

with this commit gives:


Instruction does not dominate all uses!
  %25 = trunc i32 %offset.idx16 to i16
  %broadcast.splatinsert17 = insertelement <4 x i16> undef, i16 %25, i32 0
LLVM ERROR: Broken function found, compilation aborted!


Looking at the output after the loop vectorizer we get


*** IR Dump After Loop Vectorization ***
define void @f1() {
entry:
  br i1 false, label %scalar.ph, label %vector.scevcheck

vector.scevcheck:                                 ; preds = %entry
  %mul = call { i16, i1 } @llvm.umul.with.overflow.i16(i16 1, i16 undef)
  %mul.result = extractvalue { i16, i1 } %mul, 0
  %mul.overflow = extractvalue { i16, i1 } %mul, 1
  %0 = add i16 undef, %mul.result
  %1 = sub i16 undef, %mul.result
  %2 = icmp sgt i16 %1, undef
  %3 = icmp slt i16 %0, undef
  %4 = select i1 true, i1 %2, i1 %3
  %5 = or i1 %4, %mul.overflow
  %6 = or i1 false, %5
  br i1 %6, label %scalar.ph, label %vector.ph

vector.ph:                                        ; preds = %vector.scevcheck
  %broadcast.splatinsert17 = insertelement <4 x i16> undef, i16 %25, i32 0
  %broadcast.splat18 = shufflevector <4 x i16> %broadcast.splatinsert17, <4 x
i16> undef, <4 x i32> zeroinitializer
  br label %vector.body

[...]

pred.load.continue15:                             ; preds = %pred.load.if14,
%pred.load.continue13
  %24 = phi i32 [ undef, %pred.load.continue13 ], [ %23, %pred.load.if14 ]
  %offset.idx16 = sub i32 undef, %index
  %25 = trunc i32 %offset.idx16 to i16

If we follow the path

 entry -> vector.scevcheck -> vector.ph

we see that the def of %25 in pred.load.continue15 doesn't dominate the use in
vector.ph.

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