https://llvm.org/bugs/show_bug.cgi?id=31176
Bug ID: 31176
Summary: [PowerPC] could have used a CR-setting subtract
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Backend: PowerPC
Assignee: unassignedb...@nondot.org
Reporter: spatel+l...@rotateright.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
; ret = x > y ? x-y : 0
define i32 @max(i32 %x, i32 %y) {
%sub = sub nsw i32 %x, %y
%cmp = icmp sgt i32 %x, %y
%sel = select i1 %cmp, i32 %sub, i32 0
ret i32 %sel
}
$ ./llc -o - max.ll -mtriple=powerpc64 -mattr=isel
subf 5, 4, 3 <--- use "subf."
cmpw 0, 3, 4 <--- and eliminate this cmp
li 3, 0
isel 3, 5, 3, 1
blr
There's a 2nd potential bug in this example: the 'li' could be removed because
isel RT,RA,RB,BC with RA=0 treats r0 as a zero operand?
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