[llvm] [X86] Narrow vXi32/vXi64 usubsat to vpsubusb/vpsubusw when LHS is known to fit in fewer bits (PR #206592)

[via llvm-commits]

sipher-01 wrote:

Reverted all unrelated clang-format changes in X86ISelLowering.cpp by restoring it to upstream main. The file now has no diff against upstream — our optimization lives entirely in DAGCombiner.cpp. Verified locally that usubsat-narrow.ll still passes.

~/De/p/co/o/llvm-project fix/avx512-sub-sat +1 ❯ build/bin/llvm-lit -v llvm/test/CodeGen/X86/usubsat-narrow.ll                  13s  base 04:56:17 PM
-- Testing: 1 tests, 1 workers --
PASS: LLVM :: CodeGen/X86/usubsat-narrow.ll (1 of 1)

Testing Time: 0.43s

Total Discovered Tests: 1
  Passed: 1 (100.00%)
  

https://github.com/llvm/llvm-project/pull/206592