# [InstCombine] reduce demand-limited bool math to logicfae900921b12Actions

Authored by spatel on Mar 11 2020, 11:35 AM.

# Description

[InstCombine] reduce demand-limited bool math to logic

The cmp math test is inspired by memcmp() patterns seen in D75840.
I know there's at least 1 related fold we can do here if both
values are sext'd, but I'm not seeing a way to generalize further.

We have some other bool math patterns that we want to reduce, but
that might require fixing the bogus transforms noted in D72396.

Alive proof translations of the regression tests:
https://rise4fun.com/Alive/zGWi

```Name: demand add 1
%xz = zext i1 %x to i32
%ys = sext i1 %y to i32
%sub = add i32 %xz, %ys
%r = lshr i32 %sub, 31
=>
%notx = xor i1 %x, 1
%and = and i1 %y, %notx
%r = zext i1 %and to i32

Name: demand add 2
%xz = zext i1 %x to i5
%ys = sext i1 %y to i5
%sub = add i5 %xz, %ys
%r = and i5 %sub, 16
=>
%notx = xor i1 %x, 1
%and = and i1 %y, %notx
%r = select i1 %and, i5 -16, i5 0

Name: demand add 3
%xz = zext i1 %x to i8
%ys = sext i1 %y to i8
%a = add i8 %ys, %xz
%r = ashr i8 %a, 7
=>
%notx = xor i1 %x, 1
%and = and i1 %y, %notx
%r = sext i1 %and to i8

Name: cmp math
%gt = icmp ugt i32 %x, %y
%lt = icmp ult i32 %x, %y
%xz = zext i1 %gt to i32
%yz = zext i1 %lt to i32
%s = sub i32 %xz, %yz
%r = lshr i32 %s, 31
=>
%r = zext i1 %lt to i32```

Differential Revision: https://reviews.llvm.org/D75961

# Details

Committed
 spatel Mar 11 2020, 12:45 PM
Differential Revision
D75961: [InstCombine] reduce demand-limited bool math to logic
Parents
rGfa8c4c7ffa92: [InstCombine] add tests for bool math; NFC
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