[LLVMbugs] [Bug 14725] New: loop vectorizer borks phi node

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=14725

             Bug #: 14725
           Summary: loop vectorizer borks phi node
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Loop Optimizer
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: nlewycky at google.com
                CC: llvmbugs at cs.uiuc.edu, nrotem at apple.com
    Classification: Unclassified


This testcase causes "opt -loop-vectorizer -mtriple x86_64-unknown-linux-gnu"
to emit bad IR:

target datalayout =
"e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128" 
target triple = "x86_64-unknown-linux-gnu" 

%type1 = type { %type2 } 
%type2 = type { [0 x i8*], i8**, i32, i32, i32 } 

define void @test() nounwind uwtable align 2 { 
  br label %for.body.lr.ph.i.i.i 

for.body.lr.ph.i.i.i: 
  br label %for.body.i.i.i 

for.body.i.i.i: 
  %indvars.iv = phi i64 [ %indvars.iv.next, %for.inc.i.i.i ], [ 0,
%for.body.lr\
.ph.i.i.i ] 
  br label %for.inc.i.i.i 

for.inc.i.i.i: 
  %indvars.iv.next = add i64 %indvars.iv, 1 
  %lftr.wideiv = trunc i64 %indvars.iv.next to i32 
  %exitcond = icmp ne i32 %lftr.wideiv, undef 
  br i1 %exitcond, label %for.body.i.i.i, label %for.end.i.i.i 

for.end.i.i.i: 
  %lcssa = phi %type1* [ undef, %for.inc.i.i.i ] 
  unreachable 
} 

The IR out of opt would fail the verifier. Here it is:

target datalayout =
"e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f3
target triple = "x86_64-unknown-linux-gnu"

%type1 = type { %type2 }
%type2 = type { [0 x i8*], i8**, i32, i32, i32 }

define void @test() nounwind uwtable align 2 {
  br label %for.body.lr.ph.i.i.i

for.body.lr.ph.i.i.i:                             ; preds = %0
  %zext.cnt = zext i32 undef to i64
  %end.idx = add i64 %zext.cnt, 0
  %n.mod.vf = urem i64 %zext.cnt, 8
  %n.vec = sub i64 %zext.cnt, %n.mod.vf
  %end.idx.rnd.down = add i64 %n.vec, 0
  %cmp.zero = icmp eq i64 %end.idx.rnd.down, 0
  br i1 %cmp.zero, label %middle.block, label %vector.ph

vector.ph:                                        ; preds =
%for.body.lr.ph.i.i.
  br label %vector.body

vector.body:                                      ; preds = %vector.body,
%vecto
  %index = phi i64 [ 0, %vector.ph ], [ %index.next, %vector.body ]
  %1 = insertelement <8 x i64> undef, i64 %index, i32 0
  %broadcast = shufflevector <8 x i64> %1, <8 x i64> undef, <8 x i32>
zeroinitia
  %induction = add <8 x i64> %broadcast, <i64 0, i64 1, i64 2, i64 3, i64 4,
i64
  %2 = add <8 x i64> %induction, <i64 1, i64 1, i64 1, i64 1, i64 1, i64 1, i64 
  %3 = trunc <8 x i64> %2 to <8 x i32>
  %4 = icmp ne <8 x i32> %3, undef
  %index.next = add i64 %index, 8
  %5 = icmp eq i64 %index.next, %end.idx.rnd.down
  br i1 %5, label %middle.block, label %vector.body

middle.block:                                     ; preds = %vector.body,
%for.b
  %resume.val = phi i64 [ 0, %for.body.lr.ph.i.i.i ], [ %end.idx.rnd.down,
%vect
  %cmp.n = icmp eq i64 %end.idx, %resume.val
  br i1 %cmp.n, label %for.end.i.i.i, label %scalar.ph

scalar.ph:                                        ; preds = %middle.block
  br label %for.body.i.i.i

for.body.i.i.i:                                   ; preds = %for.inc.i.i.i,
%sca
  %indvars.iv = phi i64 [ %indvars.iv.next, %for.inc.i.i.i ], [ %resume.val,
%sc
  br label %for.inc.i.i.i

for.inc.i.i.i:                                    ; preds = %for.body.i.i.i
  %indvars.iv.next = add i64 %indvars.iv, 1
  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
  %exitcond = icmp ne i32 %lftr.wideiv, undef
  br i1 %exitcond, label %for.body.i.i.i, label %for.end.i.i.i

for.end.i.i.i:                                    ; preds = %middle.block,
%for.
  %lcssa = phi %type1* [ undef, %for.inc.i.i.i ]
  unreachable
}

where the verifier error is right at the end on %lcssa, in the last BB:

PHINode should have one entry for each predecessor of its parent basic block!
  %lcssa = phi %type1* [ undef, %for.inc.i.i.i ]

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