[PATCH] D42258: [X86][SSE] Aggressively use PMADDWD for v4i32 multiplies with 17 or more leading zeros

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: craig.topper, pcordes, zvi, andreadb, spatel.

As discussed in https://reviews.llvm.org/D41484, PMADDWD for 'zero extended' vXi32 is nearly always a better option than PMULLD:
On SNB it will result in code that isn't any faster, but not any slower so we may as well keep it.
On KNL it only has half the throughput, so I've disabled it on there - ideally there'd be a better way than this.


Repository:
  rL LLVM

https://reviews.llvm.org/D42258

Files:
  lib/Target/X86/X86ISelLowering.cpp
  test/CodeGen/X86/promote.ll
  test/CodeGen/X86/shrink_vmul.ll
  test/CodeGen/X86/slow-pmulld.ll

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