[llvm-bugs] [Bug 40869] New: [X86] Poor broadcast folding from ext/trunc loads

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=40869

            Bug ID: 40869
           Summary: [X86] Poor broadcast folding from ext/trunc loads
           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

e.g. (from vector-shuffle-512-v32.ll)

llc < %s -mtriple=x86_64-apple-darwin -mcpu=skx 

define <32 x i16> @insert_dup_elt1_mem_v32i16_i32(i32* %ptr) #0 {
; KNL-LABEL: insert_dup_elt1_mem_v32i16_i32:
; KNL:       ## %bb.0:
; KNL-NEXT:    vpbroadcastw 2(%rdi), %ymm0
; KNL-NEXT:    vmovdqa %ymm0, %ymm1
; KNL-NEXT:    retq
;
; SKX-LABEL: insert_dup_elt1_mem_v32i16_i32:
; SKX:       ## %bb.0:
; SKX-NEXT:    movzwl 2(%rdi), %eax
; SKX-NEXT:    vpbroadcastw %eax, %zmm0
; SKX-NEXT:    retq
  %tmp = load i32, i32* %ptr, align 4
  %tmp1 = insertelement <4 x i32> zeroinitializer, i32 %tmp, i32 0
  %tmp2 = bitcast <4 x i32> %tmp1 to <8 x i16>
  %tmp3 = shufflevector <8 x i16> %tmp2, <8 x i16> undef, <32 x i32> <i32 1,
i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1,
i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1,
i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1>
  ret <32 x i16> %tmp3
}

Notice how the KNL (AVX2) version manages to fold but SKX (AVX512BWVL) ymm
broadcasts fail.

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