[LLVMbugs] [Bug 17792] New: llvm X86 backend generates long nop instructions for processors that don't support them

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=17792

            Bug ID: 17792
           Summary: llvm X86 backend generates long nop instructions for
                    processors that don't support them
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: mikulas at artax.karlin.mff.cuni.cz
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

When generating code for some 586 processors (including k6, winchip, via c3),
NOPL or NOPW instruction 0F 1F is generated. This causes crash because 586
processors don't support the NOPL and NOPW instruction.

For example, this program:
#include <stdio.h>

int main(void)
{
        int i;
        for (i = 0; i < 1000; i++)
                printf("%d\n", i);
        return 0;
}
when compiled with "clang -O2 loop.c -march=k6-2" results in this code:
08048420 <main>:
 8048420:       56                      push   %esi
 8048421:       83 ec 08                sub    $0x8,%esp
 8048424:       31 f6                   xor    %esi,%esi
 8048426:       66 2e 0f 1f 84 00 00    nopw   %cs:0x0(%eax,%eax,1)
 804842d:       00 00 00
 8048430:       89 74 24 04             mov    %esi,0x4(%esp)
 8048434:       c7 04 24 e0 84 04 08    movl   $0x80484e0,(%esp)
 804843b:       e8 c0 fe ff ff          call   8048300 <printf at plt>
 8048440:       46                      inc    %esi
 8048441:       81 fe e8 03 00 00       cmp    $0x3e8,%esi
 8048447:       75 e7                   jne    8048430 <main+0x10>
 8048449:       31 c0                   xor    %eax,%eax
 804844b:       83 c4 08                add    $0x8,%esp
 804844e:       5e                      pop    %esi
 804844f:       c3                      ret

The K6 processor doesn't support the nopw instruction, so the program crashes.

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20131103/c53695cb/attachment.html>