[PATCH] D25913: [InstCombine] Fold nuw left-shifts in `ugt`/`ule` comparisons.

[bryant via llvm-commits]

bryant marked 2 inline comments as done.
bryant added inline comments.


================
Comment at: test/Transforms/InstCombine/icmp-shl-zext-simplify.ll:37
+; CHECK-LABEL: @icmp_ule_i64x2(
+; CHECK-NEXT:    [[TMP2:%.*]] = trunc <2 x i64> %0 to <2 x i48>
+; CHECK-NEXT:    [[D:%.*]] = icmp eq <2 x i48> [[TMP2]], zeroinitializer
----------------
This `trunc` bothers me. On X86, I think it generates an extra `pand`:

```
.LCPI3_0:
        .short  65535                   # 0xffff
        .short  65535                   # 0xffff
        .short  65535                   # 0xffff
        .short  0                       # 0x0
        .short  65535                   # 0xffff
        .short  65535                   # 0xffff
        .short  65535                   # 0xffff
        .short  0                       # 0x0
        .text
        .globl  icmp_ule_i64x2
        .p2align        4, 0x90
        .type   icmp_ule_i64x2, at function
icmp_ule_i64x2:                         # @icmp_ule_i64x2
        .cfi_startproc
# BB#0:
        pand    .LCPI3_0(%rip), %xmm0      # <=======
        pxor    %xmm1, %xmm1
        pcmpeqd %xmm0, %xmm1
        pshufd  $177, %xmm1, %xmm0      # xmm0 = xmm1[1,0,3,2]
        pand    %xmm1, %xmm0
        retq
```

The same goes for `icmp_ule_64`, but no extra X86 op is generated in that case.


Repository:
  rL LLVM

https://reviews.llvm.org/D25913