[llvm-bugs] [Bug 25684] New: SDAG failure on AVX512BW/AVX512VL

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=25684

            Bug ID: 25684
           Summary: SDAG failure on AVX512BW/AVX512VL
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: congh at google.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

LLVM fails to select instructions for the following IR on AVX512BW/AVX512VL (OK
on other AVX512 sets):

define void @truncate_v16i16_to_v16i8(<16 x i16> %a) {
  %1 = trunc <16 x i16> %a to <16 x i8>
  store <16 x i8> %1, <16 x i8>* undef, align 4
  ret void
}



The error message on AVX512BW:


    .section    __TEXT,__text,regular,pure_instructions
LLVM ERROR: Cannot select: t9: ch = store<ST16[undef](align=4), trunc to v16i8>
t0, t2, undef:i64, undef:i64
  t2: v16i16,ch = CopyFromReg t0, Register:v16i16 %vreg0
    t1: v16i16 = Register %vreg0
  t4: i64 = undef
  t4: i64 = undef
In function: truncate_v16i16_to_v16i8



The error message on AVX512VL:


    .section    __TEXT,__text,regular,pure_instructions
LLVM ERROR: Cannot select: t6: ch = store<ST16[undef](align=4)> t0, t10,
undef:i64, undef:i64
  t10: v16i8 = X86ISD::VTRUNC t9
    t9: v16i32 = X86ISD::VSEXT t2
      t2: v16i16,ch = CopyFromReg t0, Register:v16i16 %vreg0
        t1: v16i16 = Register %vreg0
  t4: i64 = undef
  t4: i64 = undef
In function: truncate_v16i16_to_v16i8

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