[LLVMbugs] [Bug 7806] New: MIC (Modified immediate constants) field is not honored in ARM JIT's Code emitter

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=7806

           Summary: MIC (Modified immediate constants) field is not
                    honored in ARM JIT's Code emitter
           Product: libraries
           Version: trunk
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: ARM
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: sliao at google.com
                CC: llvmbugs at cs.uiuc.edu


See the repro case in the attached file. The file is generated by "clang
-emit-llvm -c "llvm_builtins.c" -o "llvm_builtins.bc". Then you can repro it
using a simple testing JIT that parses the file as module, create EE from it
and get function pointer from EE.

See the highlighted instruction below. The JIT tried incorrectly to calculate
the address for 0x100 + 0x404700e0 + 8 == 0x404701e8. But it's wrong, because
in the "0x100", "1" is treated as rotating amount, according to A5.2.4 of the
ARM Architecture Reference Manual.

float Loop(float * inputs, float count)
{
   float i = 0;
   do
   {
       float a = i * inputs[0];

       // this is the offending statement
       a += i < count ? 1.0f : 0;
       // the selection causes it to load 0 or 1 from end of function by
       // doing something like:
//        0x404700c0:e3a07000 b5        mov     r7, #0
//        0x404700c4:eef40ac0 258 vcmpe.f32     s1, s0
//        0x404700c8:eef1fa10 70  vmrs  apsr_nzcv, fpscr
//        0x404700cc:e2411001 162       sub     r1, r1, #1
//        0x404700d0:43a07001 b5  movmi r7, #1
//        0x404700d4:e3570000 54  cmp   r7, #0
//        0x404700d8:e3a07000 b5  mov   r7, #0
//        0x404700dc:13a07004 b5        movne   r7, #4
//********0x404700e0:e28f8100 15        add     r8, pc, #0    # The JIT tried
incorrectly to jump to 0x100 + 0x404700e0 + 8 == 0x404701e8. But it's wrong,
because for "0x100", "1" is treated as rotating amount, according to A5.2.4.
//        0x404700e4:ed902a00 332 vldr.32       s4, [r0]
//        0x404700e8:e3510000 54        cmp     r1, #0
//        0x404700ec:e0887007 16        add     r7, r8, r7
//        0x404700f0:edd71a00 332 vldr.32       s3, [r7]
//
//        0x404701e0:e8bd81f0 8a        pop     {r4, r5, r6, r7, r8, pc}       
*       *       *******
//        0x404701e4:0 1b       andeq   r0, r0, r0
//        0x404701e8:0 1b       andeq   r0, r0, r0
//        0x404701ec:3f800000 165       svclo   #8388608 // 1.0f
//        0x404701f0:3e99999a be        mrclo   p9, #4, r9, cr9, cr10, #4

       // padding to make the body bigger than 256 bytes
       a += inputs[2 * (int)i];
       a += inputs[3 * (int)i];
       a -= inputs[4 * (int)i];
       a += inputs[8 * (int)i];
       a -= inputs[4 * (int)i];
       a += inputs[8 * (int)i];
       a -= inputs[9 * (int)i];
       a += inputs[14 * (int)i];
       a += inputs[22 * (int)i];
       a += inputs[33 * (int)i];
       a -= inputs[44 * (int)i];
       a += inputs[28 * (int)i];
       a -= inputs[34 * (int)i];
       a += inputs[48 * (int)i];
       a -= inputs[59 * (int)i];
       inputs[(int)i] = a;

       i += 0.3f;

   } while (i < 0.922f);
   return i;
}

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