[PATCH] D24343: [X86][SSE] Improve recognition of uitofp conversions that can be performed as sitofp

[Simon Pilgrim via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: eli.friedman, delena, zvi, andreadb, spatel.
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With D24253 we can now use SelectionDAG::SignBitIsZero with vector operations.

This patch uses SelectionDAG::SignBitIsZero to recognise that a zero sign bit means that we can use a sitofp instead of a uitofp (which is not directly support on pre-AVX512 hardware).

While AVX512 does provide support for uitofp, the conversion to sitofp should not cause any regressions.

Repository:
  rL LLVM

https://reviews.llvm.org/D24343

Files:
  lib/CodeGen/SelectionDAG/SelectionDAG.cpp
  lib/Target/X86/X86ISelLowering.cpp
  test/CodeGen/X86/avx512-cvt.ll
  test/CodeGen/X86/i64-to-float.ll
  test/CodeGen/X86/uint_to_fp-3.ll
  test/CodeGen/X86/vec_int_to_fp.ll

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