[all-commits] [llvm/llvm-project] fa8656: [greedyalloc] Return early when there is no regist...

[Luo, Yuanke via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: fa8656d28d795a45dd76f5ca6030c5eef4c7003a
      https://github.com/llvm/llvm-project/commit/fa8656d28d795a45dd76f5ca6030c5eef4c7003a
  Author: Luo, Yuanke <yuanke.luo at intel.com>
  Date:   2022-06-30 (Thu, 30 Jun 2022)

  Changed paths:
    M llvm/lib/CodeGen/RegAllocGreedy.cpp
    M llvm/lib/CodeGen/RegAllocGreedy.h

  Log Message:
  -----------
  [greedyalloc] Return early when there is no register to allocate.

In X86 we split greddy register allocation into 2 passes. The 1st pass
is to allocate tile register, and the 2nd pass is to allocate the rest
of virtual register. In most cases there is no tile register, so the 1st
pass is unnecessary. To improve the compiling time, we check if there is
any register need to be allocated by invoking callback
`ShouldAllocateClass`. If there is no register to be allocated, just
return false in the pass. This would improve the 1st greed RA pass for
normal cases.

Differential Revision: https://reviews.llvm.org/D128804