[PATCH] D24345: [X86][SSE] Improve recognition of i64 sitofp conversions can be performed as i32 (PR29078)

[Simon Pilgrim via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: eli.friedman, mkuper, zvi, andreadb, spatel.
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Until AVX512DQ we only support i64/vXi64 sitofp conversion as scalars.

This patch sees if the sign bit extends far enough that we can truncate to a i32 type and then perform sitofp without loss of precision.

Sibling patch to D24343 - once that is applied the uitofp equivalent tests will reduce with this patch as well.

Note: the signum64a codegen change is an interesting one, it looks we could improve this if we updated truncateVectorCompareWithPACKSS to support 64-bit vector outputs.

Repository:
  rL LLVM

https://reviews.llvm.org/D24345

Files:
  lib/Target/X86/X86ISelLowering.cpp
  test/CodeGen/X86/i64-to-float.ll
  test/CodeGen/X86/sse-fsignum.ll

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