[llvm-bugs] [Bug 29079] New: [X86][SSE] Failure to recognise uitofp conversions that can be performed as sitofp

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=29079

            Bug ID: 29079
           Summary: [X86][SSE] Failure to recognise uitofp conversions
                    that can be performed as sitofp
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: llvm-dev at redking.me.uk
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Related to [Bugzilla #29078]. If we have masked the sign bits of an integer
source then we can safely replace (slow) uitofp conversions with sitofp. 

Note that it'd be even better if we can handle non-uniform masks!

define <4 x float> @mask_ucvt_4i32_4f32(<4 x i32> %a) {
  %and = and <4 x i32> %a, <i32 255, i32 255, i32 255, i32 255>
  %cvt = uitofp <4 x i32> %and to <4 x float>
  ret <4 x float> %cvt
}

define <4 x double> @mask_ucvt_4i32_4f64(<4 x i32> %a) {
  %and = and <4 x i32> %a, <i32 255, i32 255, i32 4095, i32 65595>
  %cvt = uitofp <4 x i32> %and to <4 x double>
  ret <4 x double> %cvt
}

"~/LLVM/build/bin/llc -mcpu=btver2"

_mask_ucvt_4i32_4f32:vpand   LCPI0_0(%rip), %xmm0, %xmm0
        vpblendw        $170, LCPI0_1(%rip), %xmm0, %xmm1 ## xmm1 =
xmm0[0],mem[1],xmm0[2],mem[3],xmm0[4],mem[5],xmm0[6],mem[7]
        vpsrld  $16, %xmm0, %xmm0
        vpblendw        $170, LCPI0_2(%rip), %xmm0, %xmm0 ## xmm0 =
xmm0[0],mem[1],xmm0[2],mem[3],xmm0[4],mem[5],xmm0[6],mem[7]
        vaddps  LCPI0_3(%rip), %xmm0, %xmm0
        vaddps  %xmm0, %xmm1, %xmm0
        retq

_mask_ucvt_4i32_4f64:
        vpand   LCPI1_0(%rip), %xmm0, %xmm0
        vpand   LCPI1_1(%rip), %xmm0, %xmm1
        vpsrld  $16, %xmm0, %xmm0
        vcvtdq2pd       %xmm0, %ymm0
        vmulpd  LCPI1_2(%rip), %ymm0, %ymm0
        vcvtdq2pd       %xmm1, %ymm1
        vaddpd  %ymm1, %ymm0, %ymm0
        retq

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