[llvm-bugs] [Bug 39178] New: [X86] SimplifyDemandedBits failure to simplify PMULDQ/PMULUDQ

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=39178

            Bug ID: 39178
           Summary: [X86] SimplifyDemandedBits failure to simplify
                    PMULDQ/PMULUDQ
           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: andrea.dibiagio at gmail.com, craig.topper at gmail.com,
                    llvm-bugs at lists.llvm.org, spatel+llvm at rotateright.com

define <2 x i64> @muludq_demanded_bits(<4 x i32>, <4 x i32>) {
  %3 = shufflevector <4 x i32> %0, <4 x i32> <i32 undef, i32 0, i32 undef, i32
0>, <4 x i32> <i32 0, i32 5, i32 2, i32 7>
  %4 = shufflevector <4 x i32> %1, <4 x i32> <i32 undef, i32 0, i32 undef, i32
0>, <4 x i32> <i32 0, i32 5, i32 2, i32 7>
  %5 = bitcast <4 x i32> %3 to <2 x i64>
  %6 = bitcast <4 x i32> %4 to <2 x i64>
  %7 = mul <2 x i64> %6, %5
  ret <2 x i64> %7
}

llc -mcpu=btver2

vpxor   %xmm2, %xmm2, %xmm2
vpblendw        $204, %xmm2, %xmm0, %xmm0 # xmm0 =
xmm0[0,1],xmm2[2,3],xmm0[4,5],xmm2[6,7]
vpblendw        $204, %xmm2, %xmm1, %xmm1 # xmm1 =
xmm1[0,1],xmm2[2,3],xmm1[4,5],xmm2[6,7]
vpmuludq        %xmm0, %xmm1, %xmm0
retq

The vpblendw can be removed as PMULDQ/PMULUDQ only use the bottom 32-bits of
each i64 element

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