[llvm-bugs] [Bug 38649] New: multiply lowering of divide-by-constant doesn't occur on haswell

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=38649

            Bug ID: 38649
           Summary: multiply lowering of divide-by-constant doesn't occur
                    on haswell
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: jorg.brown at gmail.com
                CC: llvm-bugs at lists.llvm.org

Source:

struct SecsAndTicks {
  uint64_t seconds;
  uint32_t ticks;
};

SecsAndTicks DivBy4Bill(uint64_t tix) {
  return {tix / 4000000000,
          uint32_t(tix % 4000000000)};
}

x86-64 codegen:
        movq    %rdi, %rax
        shrq    $11, %rax
        movabsq $4835703278458517, %rcx # imm = 0x112E0BE826D695
        mulq    %rcx
        shrq    $9, %rdx
        imull   $-294967296, %edx, %eax # imm = 0xEE6B2800
        subl    %eax, %edi
        movq    %rdx, %rax
        movl    %edi, %edx
        retq

march=haswell codegen:
        movl    $4000000000, %ecx       # imm = 0xEE6B2800
        movq    %rdi, %rax
        shrq    $32, %rax
        je      .LBB0_1
        xorl    %edx, %edx
        movq    %rdi, %rax
        divq    %rcx
        retq
.LBB0_1:
        xorl    %edx, %edx
        movl    %edi, %eax
        divl    %ecx
        retq

See https://godbolt.org/g/qGTDGN for repro

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