[llvm] [SelectionDAG] Improve wide integer squaring (PR #226403)

[via llvm-commits]

github-actions[bot] wrote:

<!--PREMERGE ADVISOR COMMENT: Windows-->
# :window: Windows x64 Test Results

* 143201 tests passed
* 3417 tests skipped
* 1 test failed

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

### LLVM
<details>
<summary>LLVM.CodeGen/X86/wide-int-square.ll</summary>

```
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 2
c:\_work\llvm-project\llvm-project\build\bin\llc.exe < C:\_work\llvm-project\llvm-project\llvm\test\CodeGen\X86\wide-int-square.ll -mtriple=x86_64-unknown-linux-gnu | c:\_work\llvm-project\llvm-project\build\bin\filecheck.exe C:\_work\llvm-project\llvm-project\llvm\test\CodeGen\X86\wide-int-square.ll --check-prefix=X64
# executed command: 'c:\_work\llvm-project\llvm-project\build\bin\llc.exe' -mtriple=x86_64-unknown-linux-gnu
# note: command had no output on stdout or stderr
# executed command: 'c:\_work\llvm-project\llvm-project\build\bin\filecheck.exe' 'C:\_work\llvm-project\llvm-project\llvm\test\CodeGen\X86\wide-int-square.ll' --check-prefix=X64
# .---command stderr------------
# | C:\_work\llvm-project\llvm-project\llvm\test\CodeGen\X86\wide-int-square.ll:11:13: error: X64-NEXT: expected string not found in input
# | ; X64-NEXT: movq 8(%rsi), %r8
# |             ^
# | <stdin>:10:19: note: scanning from here
# |  movq (%rsi), %rcx
# |                   ^
# | <stdin>:11:2: note: possible intended match here
# |  movq 8(%rsi), %r9
# |  ^
# | 
# | Input file: <stdin>
# | Check file: C:\_work\llvm-project\llvm-project\llvm\test\CodeGen\X86\wide-int-square.ll
# | 
# | -dump-input=help explains the following input dump.
# | 
# | Input was:
# | <<<<<<
# |            .
# |            .
# |            .
# |            5:  .prefalign 4, .Lfunc_end0, nop 
# |            6:  .type sqr_i256, at function 
# |            7: sqr_i256: # @sqr_i256 
# |            8: # %bb.0: 
# |            9:  pushq %rbx 
# |           10:  movq (%rsi), %rcx 
# | next:11'0                      {   search range start (exclusive)
# | next:11'1                          error: no match found in search range
# |           11:  movq 8(%rsi), %r9 
# | next:11'2      ?                   possible intended match
# |           12:  movq 16(%rsi), %r11 
# |           13:  movq %rcx, %rax 
# |           14:  mulq %r11 
# |           15:  movq %rax, %r10 
# |           16:  movq 24(%rsi), %rbx 
# |            .
# |            .
# |            .
# |           45:  .size sqr_i256, .Lfunc_end0-sqr_i256 
# |           46:  # -- End function 
# |           47:  .globl sqr_i512_zext_i256 # -- Begin function sqr_i512_zext_i256 
# |           48:  .prefalign 4, .Lfunc_end1, nop 
# |           49:  .type sqr_i512_zext_i256, at function 
# |           50: sqr_i512_zext_i256: # @sqr_i512_zext_i256 
# | next:11'3                        }                        search range end (exclusive)
# |           51: # %bb.0: 
# |           52:  pushq %rbp 
# |           53:  pushq %r15 
# |           54:  pushq %r14 
# |           55:  pushq %r13 
# |            .
# |            .
# |            .
# | >>>>>>
# `-----------------------------
# 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/226403