[Bug target/86236] New: -mstackrealign prologue clobbers %edi for fastcall functions with global register variable

[fw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86236

            Bug ID: 86236
           Summary: -mstackrealign prologue clobbers %edi for fastcall
                    functions with global register variable
           Product: gcc
           Version: 8.1.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fw at gcc dot gnu.org
  Target Milestone: ---

#include <xmmintrin.h>

void f1 (void *, int);

register int edi __asm__ ("edi");

__attribute__ ((fastcall))
void
f2 (void)
{ 
  // Force stack alignment.                                                     
  __m128i m;
  f1 (&m, edi);
}


Compile with “-m32 -O2 -march=x86-64 -msse2 -mfpmath=sse -mstackrealign”:

        .globl  f2
        .type   f2, @function
f2:
.LFB504:
        .cfi_startproc
        leal    4(%esp), %edi
        .cfi_def_cfa 7, 0
        andl    $-16, %esp
        pushl   -4(%edi)
        pushl   %ebp
        .cfi_escape 0x10,0x5,0x2,0x75,0
        movl    %esp, %ebp
        pushl   %edi
        .cfi_escape 0xf,0x3,0x75,0x7c,0x6
        leal    -24(%ebp), %eax
        subl    $28, %esp
        pushl   %edi
        pushl   %eax
        call    f1
        movl    -4(%ebp), %edi
        .cfi_def_cfa 7, 0
        addl    $16, %esp
        leave
        .cfi_restore 5
        leal    -4(%edi), %esp
        .cfi_def_cfa 4, 4
        ret
        .cfi_endproc


The value of %edi is clobbered before it is saved on the stack.  I think %edi
is callee-saved even for fastcall functions, so this is wrong on multiple
levels.