[PATCH] D23253: [X86] Generalized transformation of `definstr gr8; movzx gr32, gr8` to `xor gr32, gr32; definstr gr8`

[bryant via llvm-commits]

bryant created this revision.
bryant added reviewers: llvm-commits, mkuper.
bryant set the repository for this revision to rL LLVM.

As indicated by the title, this post-register allocation pre-rewrite pass
that generalizes D21774 by matching patterns of the form,

```
gr8<def> = instr_defining_gr8  # that may or may not use eflags
gr32<def> = movzx gr8
```

into,

```
gr32 = mov32r0 eflags<imp-def>  # carefully avoids clobbering eflags
...
gr8<def> = instr_defining_gr8
```

with the goal of reducing read stalls, partial register stalls, micro-ops, and
overall binary size.

Except for a few rare cases, it never performs worse than D21774, and does
surprisingly better in other cases. IACA-annotated assembly output can be found
at https://reviews.llvm.org/P7213 (for x86-64) and at
https://reviews.llvm.org/P7214 (for x86-32).

Not all of the tests have been updated; this is still a work in progress.

Repository:
  rL LLVM

https://reviews.llvm.org/D23253

Files:
  lib/Target/X86/CMakeLists.txt
  lib/Target/X86/X86.h
  lib/Target/X86/X86FixupZExt.cpp
  lib/Target/X86/X86TargetMachine.cpp
  test/CodeGen/X86/avx-intrinsics-x86.ll
  test/CodeGen/X86/avx512-cmp.ll
  test/CodeGen/X86/cmpxchg-i1.ll
  test/CodeGen/X86/cmpxchg-i128-i1.ll
  test/CodeGen/X86/fast-isel-cmp.ll
  test/CodeGen/X86/fp128-cast.ll
  test/CodeGen/X86/fp128-compare.ll
  test/CodeGen/X86/sse42-intrinsics-fast-isel.ll
  test/CodeGen/X86/sse42-intrinsics-x86.ll

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