[llvm-bugs] [Bug 52049] New: Missing combine of shl+bswap to rol

via llvm-bugs llvm-bugs at lists.llvm.org
Sun Oct 3 03:01:39 PDT 2021


            Bug ID: 52049
           Summary: Missing combine of shl+bswap to rol
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: david.bolvansky at gmail.com
                CC: llvm-bugs at lists.llvm.org

unsigned read_be16 (unsigned char *data)
  return *(data + 1) | (*data << 8);

read_be16(unsigned char*):                         # @read_be16(unsigned char*)
        movzx   eax, word ptr [rdi]
        shl     eax, 16
        bswap   eax

read_be16(unsigned char*):
        movzx   eax, WORD PTR [rdi]
        rol     ax, 8
        movzx   eax, ax


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