[llvm] [Instcombine] Lower to explicit subtraction + unsigned comparison (PR #170896)

[via llvm-commits]

github-actions[bot] wrote:

<!--PREMERGE ADVISOR COMMENT: Linux-->
# :penguin: Linux x64 Test Results

* 166845 tests passed
* 2910 tests skipped
* 1 test failed

## Failed Tests
(click on a test name to see its output)

### Clang
<details>
<summary>Clang.CodeGen/builtins-multiprecision.c</summary>

```
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
/home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/clang -cc1 -internal-isystem /home/gha/actions-runner/_work/llvm-project/llvm-project/build/lib/clang/22/include -nostdsysteminc -triple "i686-unknown-unknown"   -emit-llvm -x c /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/CodeGen/builtins-multiprecision.c -o - -O3 | /home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/FileCheck /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/CodeGen/builtins-multiprecision.c
# executed command: /home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/clang -cc1 -internal-isystem /home/gha/actions-runner/_work/llvm-project/llvm-project/build/lib/clang/22/include -nostdsysteminc -triple i686-unknown-unknown -emit-llvm -x c /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/CodeGen/builtins-multiprecision.c -o - -O3
# note: command had no output on stdout or stderr
# executed command: /home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/FileCheck /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/CodeGen/builtins-multiprecision.c
# .---command stderr------------
# | /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/CodeGen/builtins-multiprecision.c:101:12: error: CHECK: expected string not found in input
# |  // CHECK: %{{.+}} = {{.*}} call { i8, i1 } @llvm.usub.with.overflow.i8(i8 %x, i8 %y)
# |            ^
# | <stdin>:94:55: note: scanning from here
# | define dso_local zeroext range(i8 0, 2) i8 @test_subcb(i8 noundef zeroext %x, i8 noundef zeroext %y, i8 noundef zeroext %carryin, ptr noundef writeonly captures(none) initializes((0, 1)) %z) local_unnamed_addr #0 {
# |                                                       ^
# | 
# | Input file: <stdin>
# | Check file: /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/CodeGen/builtins-multiprecision.c
# | 
# | -dump-input=help explains the following input dump.
# | 
# | Input was:
# | <<<<<<
# |            .
# |            .
# |            .
# |           89:  
# |           90: ; Function Attrs: mustprogress nocallback nocreateundeforpoison nofree nosync nounwind speculatable willreturn memory(none) 
# |           91: declare { i64, i1 } @llvm.uadd.with.overflow.i64(i64, i64) #1 
# |           92:  
# |           93: ; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: write) 
# |           94: define dso_local zeroext range(i8 0, 2) i8 @test_subcb(i8 noundef zeroext %x, i8 noundef zeroext %y, i8 noundef zeroext %carryin, ptr noundef writeonly captures(none) initializes((0, 1)) %z) local_unnamed_addr #0 { 
# | check:101                                                           X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
# |           95: entry: 
# | check:101     ~~~~~~~
# |           96:  %0 = sub i8 %x, %y 
# | check:101     ~~~~~~~~~~~~~~~~~~~~
# |           97:  %1 = icmp ult i8 %x, %y 
# | check:101     ~~~~~~~~~~~~~~~~~~~~~~~~~
# |           98:  %2 = sub i8 %0, %carryin 
# | check:101     ~~~~~~~~~~~~~~~~~~~~~~~~~~
# |           99:  %3 = icmp ult i8 %0, %carryin 
# | check:101     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# |            .
# |            .
# |            .
# | >>>>>>
# `-----------------------------
# error: command failed with exit status: 1

--

```
</details>

If these failures are unrelated to your changes (for example tests are broken or flaky at HEAD), please open an issue at https://github.com/llvm/llvm-project/issues and add the `infrastructure` label.

https://github.com/llvm/llvm-project/pull/170896