[llvm-bugs] [Bug 42457] New: [InstCombine] `x - ~(y)` vs `x + y + 1`
via llvm-bugs
llvm-bugs at lists.llvm.org
Sun Jun 30 15:21:42 PDT 2019
https://bugs.llvm.org/show_bug.cgi?id=42457
Bug ID: 42457
Summary: [InstCombine] `x - ~(y)` vs `x + y + 1`
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: unassignedbugs at nondot.org
Reporter: lebedev.ri at gmail.com
CC: llvm-bugs at lists.llvm.org
https://godbolt.org/z/2N-IRy
https://rise4fun.com/Alive/WMn
int bad(unsigned x, unsigned y) {
return x - ~(y);
}
int good(unsigned x, unsigned y) {
return x + y + 1;
}
Name:
%o = xor i32 %y, -1
%r = sub i32 %x, %o
=>
%n = add i32 %y, 1
%r = add i32 %x, %n
We currently don't prefer any one to other, should we?
I'd guess we want the variant with 2 adds?
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