[LLVMbugs] [Bug 21365] Mesa llvmpipe lp_test_format regression with llvm-3.6.0svn

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Fri Oct 24 11:53:09 PDT 2014


Jose Fonseca <jfonseca at vmware.com> changed:

           What    |Removed                     |Added
             Status|NEW                         |RESOLVED
         Resolution|---                         |INVALID

--- Comment #1 from Jose Fonseca <jfonseca at vmware.com> ---
This might not be a regressions in LLVM per se, but rather a LLVM change
exposing a pre-existing bug in this test.

$ gdb --args ./lp_test_format -v -v

define void @fetch_r32g32b32a32_float_float(<4 x float>*, i8*, i32, i32) {
  %4 = getelementptr i8* %1, i32 0
  %5 = bitcast i8* %4 to i128*
  %6 = load i128* %5
  %7 = bitcast i128 %6 to <4 x float>
  store <4 x float> %7, <4 x float>* %0
  ret void

     0:        pushq    %rbp
     1:        movq    %rsp, %rbp
     4:        vmovaps    (%rsi), %xmm0
     8:        vmovaps    %xmm0, (%rdi)
    12:        popq    %rbp
    13:        retq

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7ff7004 in ?? ()
(gdb) bt
#0  0x00007ffff7ff7004 in ?? ()
#1  0x00007fffffffe210 in ?? ()
#2  0x0000000000407174 in test_format_float (verbose=0, fp=0x7fffffffe160,
desc=0x217fdf0) at src/gallium/drivers/llvmpipe/lp_test_format.c:168
Backtrace stopped: frame did not save the PC
(gdb) disassemble 0x00007ffff7ff7000,0x00007ffff7ff7010
Dump of assembler code from 0x7ffff7ff7000 to 0x7ffff7ff7010:
   0x00007ffff7ff7000:    push   %rbp
   0x00007ffff7ff7001:    mov    %rsp,%rbp
=> 0x00007ffff7ff7004:    vmovaps (%rsi),%xmm0
   0x00007ffff7ff7008:    vmovaps %xmm0,(%rdi)
   0x00007ffff7ff700c:    pop    %rbp
   0x00007ffff7ff700d:    retq   
   0x00007ffff7ff700e:    add    %al,(%rax)
End of assembler dump.
(gdb) p /x $rsi
$2 = 0x1271e2c

The code generated by LLVM looks fine.  The problem is that caller is not
passing an aligned vector.

It seems that before, LLVM would generate the following assembly for the same

     0:        pushq    %rbp
     1:        movq    %rsp, %rbp
     4:        movq    (%rsi), %rax
     7:        movq    8(%rsi), %rcx
    11:        movq    %rcx, 8(%rdi)
    15:        movq    %rax, (%rdi)
    18:        popq    %rbp
    19:        retq

hence avoiding the problem.

In other words, Vinson, I think we should close this issue and file another on
FDO bug tracker.

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