https://bugs.llvm.org/show_bug.cgi?id=47133
Bug ID: 47133
Summary: Incorrect mul foo, undef -> shl foo, undef
Product: libraries
Version: trunk
Hardware: All
OS: All
Status: NEW
Keywords: miscompilation
Severity: normal
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: nunoplo...@sapo.pt
CC: lebedev...@gmail.com, llvm-bugs@lists.llvm.org,
llvm-...@redking.me.uk, reg...@cs.utah.edu
This is a recent regression in Transforms/InstCombine/mul.ll.
shl foo, undef is poison, so we can't introduce that.
define <2 x i32> @mulsub1_vec_nonuniform_undef(<2 x i32> %a0, <2 x i32> %a1) {
%sub = sub <2 x i32> %a1, %a0
%mul = mul <2 x i32> %sub, { 4294967292, undef }
ret <2 x i32> %mul
}
=>
define <2 x i32> @mulsub1_vec_nonuniform_undef(<2 x i32> %a0, <2 x i32> %a1) {
%sub.neg = sub <2 x i32> %a0, %a1
%mul = shl <2 x i32> %sub.neg, { 2, undef }
ret <2 x i32> %mul
}
Transformation doesn't verify!
ERROR: Target is more poisonous than source
Example:
<2 x i32> %a0 = < undef, undef >
<2 x i32> %a1 = < undef, undef >
Source:
<2 x i32> %sub = < undef, undef >
<2 x i32> %mul = < #x00000000 (0), #x00000000 (0) >
Target:
<2 x i32> %sub.neg = < #x00000000 (0), #x00000000 (0) >
<2 x i32> %mul = < #x00000000 (0), poison >
Source value: < #x00000000 (0), #x00000000 (0) >
Target value: < #x00000000 (0), poison >
Probably caused by
https://github.com/llvm/llvm-project/commit/0c1c756a31536666a7b6f5bdb744dbce923a0c9e
https://web.ist.utl.pt/nuno.lopes/alive2/index.php?hash=b697cc49b7cc411c&test=Transforms%2FInstCombine%2Fmul.ll
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