maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity

[SelectionDAG] Fold abs(undef) to 0 instead of undef. 

abs should only produce a positive value or the signed minimum
value. This means we can't fold abs(undef) to undef as that would
allow more values. Fold to 0 instead to match InstSimplify.

Fixes test mentioned in comment on pr55271.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D126174
This commit is contained in:
Craig Topper 2022-05-22 12:47:27 -07:00
parent 419e49621f
commit 768a1ca5ec
2 changed files with 16 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
View File

@ -5243,7 +5243,7 @@ SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
assert(VT.isInteger() && VT == Operand.getValueType() &&
"Invalid ABS!");
if (OpOpcode == ISD::UNDEF)
return getUNDEF(VT);
return getConstant(0, DL, VT);
break;
case ISD::BSWAP:
assert(VT.isInteger() && VT == Operand.getValueType() &&

15
llvm/test/CodeGen/X86/pr55271.ll Normal file
View File

@ -0,0 +1,15 @@
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu | FileCheck %s
; abs(undef) should fold to 0 not undef.
declare i32 @llvm.abs.i32(i32, i1 immarg) #0
define i32 @abs(i32 %0) {
; CHECK-LABEL: abs:
; CHECK: # %bb.0:
; CHECK-NEXT: xorl %eax, %eax
; CHECK-NEXT: retq
%2 = call i32 @llvm.abs.i32(i32 undef, i1 false)
ret i32 %2
}