[PATCH] D150437: [FPEnv] Get rid of extra moves in fpenv calls

[Serge Pavlov via Phabricator via llvm-commits]

sepavloff created this revision.
sepavloff added reviewers: arsenm, nikic, RKSimon, greened, craig.topper, shchenz.
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If intrinsic `get_fpenv` or `set_fpenv` is lowered to the form where FP
environment is represented as a region in memory, extra moves can
appear. For example the code:

  define void @func_01(ptr %ptr) {
    %env = call i256 @llvm.get.fpenv.i256()
    store i256 %env, ptr %ptr
    ret void
  }

produces DAG:

  ch = get_fpenv_mem ch, memory_region
  val: i256, ch = load ch, memory_region
  ch = store ch, ptr, val

In this case the extra moves can be avoided if `get_fpenv_mem` got
pointer to the memory where the FP environment should be finally placed.

This change implement such optimization for this use case.

Depends on D71742 <https://reviews.llvm.org/D71742>


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D150437

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/X86/fpenv.ll

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