[PATCH] D20774: [InstCombine] look through bitcasts to find selects

Sanjay Patel via llvm-commits llvm-commits at lists.llvm.org
Sat May 28 12:24:14 PDT 2016

spatel created this revision.
spatel added reviewers: majnemer, RKSimon, chandlerc.
spatel added a subscriber: llvm-commits.
Herald added a subscriber: mcrosier.

The motivating example for this patch is this IR produced via SSE intrinsics in C:
  define <2 x i64> @gibson(<2 x i64> %a, <2 x i64> %b) {
    %t0 = bitcast <2 x i64> %a to <4 x i32>
    %t1 = bitcast <2 x i64> %b to <4 x i32>
    %cmp = icmp sgt <4 x i32> %t0, %t1
    %sext = sext <4 x i1> %cmp to <4 x i32>
    %t2 = bitcast <4 x i32> %sext to <2 x i64>
    %and = and <2 x i64> %t2, %a
    %neg = xor <4 x i32> %sext, <i32 -1, i32 -1, i32 -1, i32 -1>
    %neg2 = bitcast <4 x i32> %neg to <2 x i64>
    %and2 = and <2 x i64> %neg2, %b
    %or = or <2 x i64> %and, %and2
    ret <2 x i64> %or

For an AVX target, this is currently:
  vpcmpgtd	%xmm1, %xmm0, %xmm2
  vpand	%xmm0, %xmm2, %xmm0
  vpandn	%xmm1, %xmm2, %xmm1
  vpor	%xmm1, %xmm0, %xmm0

With this patch, it becomes:
  vpmaxsd	%xmm1, %xmm0, %xmm0



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