[llvm-bugs] [Bug 39927] New: [InstCombine] Attempt to replace MOVMSK with zext (bitcast <X x i1> to iX) to i32

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=39927

            Bug ID: 39927
           Summary: [InstCombine] Attempt to replace MOVMSK with zext
                    (bitcast <X x i1> to iX) to i32
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: llvm-dev at redking.me.uk
                CC: craig.topper at gmail.com, llvm-bugs at lists.llvm.org,
                    llvm-dev at redking.me.uk, spatel+llvm at rotateright.com

https://godbolt.org/z/SvH3do

Very similar to what we do with SSE BLENDV cases from a comparison+sext that
can be replaced with a select, we should now be able to replace MOVMSK
intrinsics with bitcasts from the comparison result.

PMOVMSKB <X x i8>
MOVMSKPS <X x float>
MOVMSKPD <X x float>

declare i32 @llvm.x86.sse2.pmovmskb.128(<16 x i8>)

define i32 @movmsk_16i8(<16 x i8>, <16 x i8>) {
  %3 = icmp sgt <16 x i8> %0, %1
  %4 = sext <16 x i1> %3 to <16 x i8>
  %5 = tail call i32 @llvm.x86.sse2.pmovmskb.128(<16 x i8> %4)
  ret i32 %5
}

define i32 @movmsk_16i8_select(<16 x i8>, <16 x i8>) {
  %3 = icmp sgt <16 x i8> %0, %1
  %4 = bitcast <16 x i1> %3 to i16
  %5 = zext i16 %4 to i32
  ret i32 %5
}

Cases where the comparison arguments don't match the MOVMSK arguments are
trickier, but this is what I've managed so far (depending on what we do with
the MOVMSK scalar result we should be able to do a lot better):

define i32 @movmsk_8i16(<8 x i16>, <8 x i16>) {
  %3 = icmp sgt <8 x i16> %0, %1
  %4 = sext <8 x i1> %3 to <8 x i16>
  %5 = bitcast <8 x i16> %4 to <16 x i8>
  %6 = tail call i32 @llvm.x86.sse2.pmovmskb.128(<16 x i8> %5)
  ret i32 %6
}

define i32 @movmsk_8i16_select(<8 x i16>, <8 x i16>) {
  %3 = icmp sgt <8 x i16> %0, %1
  %4 = sext <8 x i1> %3 to <8 x i16>
  %5 = bitcast <8 x i16> %4 to <16 x i8>
  %6 = icmp slt <16 x i8> %5, zeroinitializer
  %7 = bitcast <16 x i1> %6 to i16
  %8 = zext i16 %7 to i32
  ret i32 %8
}

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