[llvm] [SLP] Don't truncate compare constants that change value at the demoted width (PR #209030)

[via llvm-commits]

github-actions[bot] wrote:

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

* 178753 tests passed
* 3596 tests skipped
* 1 test failed

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

### LLVM
<details>
<summary>LLVM.Transforms/SLPVectorizer/X86/minbitwidth-icmp-signed-const-trunc.ll</summary>

```
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 2
/home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/opt -passes=slp-vectorizer -S -mtriple=x86_64-unknown-linux-gnu < /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/test/Transforms/SLPVectorizer/X86/minbitwidth-icmp-signed-const-trunc.ll | /home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/FileCheck /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/test/Transforms/SLPVectorizer/X86/minbitwidth-icmp-signed-const-trunc.ll
# executed command: /home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/opt -passes=slp-vectorizer -S -mtriple=x86_64-unknown-linux-gnu
# 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/llvm/test/Transforms/SLPVectorizer/X86/minbitwidth-icmp-signed-const-trunc.ll
# .---command stderr------------
# | /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/test/Transforms/SLPVectorizer/X86/minbitwidth-icmp-signed-const-trunc.ll:16:15: error: CHECK-NEXT: expected string not found in input
# | ; CHECK-NEXT: [[TMP0:%.*]] = insertelement <8 x i16> poison, i16 [[C]], i32 0
# |               ^
# | <stdin>:9:23: note: scanning from here
# |  %or = or i32 %conv, 5
# |                       ^
# | <stdin>:9:23: note: with "C" equal to "%c"
# |  %or = or i32 %conv, 5
# |                       ^
# | <stdin>:9:23: note: pattern attempts to capture variables: "TMP0"
# |  %or = or i32 %conv, 5
# |                       ^
# | <stdin>:10:2: note: possible intended match here
# |  %0 = insertelement <8 x i16> poison, i16 %c, i64 0
# |  ^
# | 
# | Input file: <stdin>
# | Check file: /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/test/Transforms/SLPVectorizer/X86/minbitwidth-icmp-signed-const-trunc.ll
# | 
# | -dump-input=help explains the following input dump.
# | 
# | Input was:
# | <<<<<<
# |            1: ; ModuleID = '<stdin>' 
# |            2: source_filename = "<stdin>" 
# |            3: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128" 
# |            4: target triple = "x86_64-unknown-linux-gnu" 
# |            5:  
# |            6: define i1 @test(i16 %a, i16 %c) { 
# |            7: entry: 
# |            8:  %conv = sext i16 %a to i32 
# |            9:  %or = or i32 %conv, 5 
# | next:16'0                          {   search range start (exclusive)
# | next:16'1                              error: no match found in search range
# | next:16'2                              with "C" equal to "%c"
# | next:16'3                              pattern attempts to capture variables: "TMP0"
# |           10:  %0 = insertelement <8 x i16> poison, i16 %c, i64 0 
# | next:16'4      ?                                                    possible intended match
# |           11:  %1 = shufflevector <8 x i16> %0, <8 x i16> poison, <8 x i32> zeroinitializer 
# |           12:  %2 = add <8 x i16> %1, <i16 1, i16 2, i16 3, i16 4, i16 5, i16 6, i16 7, i16 8> 
# |           13:  %3 = trunc i32 %or to i16 
# |           14:  %4 = insertelement <8 x i16> poison, i16 %3, i64 0 
# |           15:  %5 = shufflevector <8 x i16> %4, <8 x i16> poison, <8 x i32> zeroinitializer 
# |            .
# |            .
# |            .
# |           22: } 
# |           23:  
# |           24: ; Function Attrs: nocallback nocreateundeforpoison nofree nosync nounwind speculatable willreturn memory(none) 
# |           25: declare i1 @llvm.vector.reduce.and.v8i1(<8 x i1>) #0 
# |           26:  
# |           27: attributes #0 = { nocallback nocreateundeforpoison nofree nosync nounwind speculatable willreturn memory(none) } 
# | next:16'5                                                                                                                      } search range end (exclusive)
# | >>>>>>
# `-----------------------------
# 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/209030