[llvm-bugs] [Bug 33741] New: llvm does not support loopw/loopl

via llvm-bugs llvm-bugs at lists.llvm.org
Tue Jul 11 01:00:54 PDT 2017


            Bug ID: 33741
           Summary: llvm does not support loopw/loopl
           Product: tools
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: TableGen
          Assignee: unassignedbugs at nondot.org
          Reporter: bonzini at gnu.org
                CC: llvm-bugs at lists.llvm.org

LLVM supports jcxz/jecxz, but doesn't allow overriding the register used by the
'loop' instruction.

// compile with:
//    clang -m32 test-loopw.c -O2 -o test-loopw
// expected output:
//    0xffff0000

#include <stdlib.h>
#include <stdio.h>

int main()
  unsigned x = 0xffff1234;
  // Intel syntax:
  //     asm volatile("1: addr16 loop 1b" : "+c" (x));
  asm volatile("1: loopw 1b" : "+c" (x));
  printf("%x\n", x);
  exit (x == 0xffff0000 ? 0 : 1);

This seems to affect the disassembler as well.  The above program is
disassembled like this:

Disassembly of section .text:
 8048354:       89 d9   movl    %ebx, %ecx
 8048356:       67 e2 fd        loop    -3

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