Re: Enable EBX for x86 in 32bits PIC code

[Vladimir Makarov <vmakarov@redhat.com>]

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On 2014-08-26 5:42 PM, Ilya Enkovich wrote:
> Hi,
>
> Here is a patch I tried.  I apply it over revision 214215.  Unfortunately I do not have a small reproducer but the problem can be easily reproduced on SPEC2000 benchmark 175.vpr.  The problem is in read_arch.c:701 where float value is compared with float constant 1.0.  It is inlined into read_arch function and can be easily found in RTL dump of function read_arch as a float comparison with 1.0 after the first call to strtod function.
>
> Here is a compilation string I use:
>
> gcc -m32 -mno-movbe -g3 -fdump-rtl-all-details -O2 -ffast-math -mfpmath=sse -m32  -march=slm -fPIE -pie -c -o read_arch.o       -DSPEC_CPU2000        read_arch.c
>
> In my final assembler comparison with 1.0 looks like:
>
> comiss  .LC11@GOTOFF(%ebp), %xmm0       # 1101  *cmpisf_sse     [length = 7]
>
> and %ebp here doesn't have a proper value.
>
> I'll try to make a smaller reproducer if these instructions don't help.

I've managed to reproduce it.  Although it would be better to send the 
patch as an attachment.

The problem is actually in IRA not LRA.  IRA splits pseudo used for PIC. 
  Then in a region when a *new* pseudo used as PIC we rematerialize a 
constant which transformed in memory addressed through *original* PIC 
pseudo.

To solve the problem we should prevent such splitting and guarantee that 
PIC pseudo allocnos in different region gets the same hard reg.

The following patch should solve the problem.



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Index: ira-color.c
===================================================================
--- ira-color.c	(revision 214576)
+++ ira-color.c	(working copy)
@@ -3239,9 +3239,10 @@
 	  ira_assert (ALLOCNO_CLASS (subloop_allocno) == rclass);
 	  ira_assert (bitmap_bit_p (subloop_node->all_allocnos,
 				    ALLOCNO_NUM (subloop_allocno)));
-	  if ((flag_ira_region == IRA_REGION_MIXED)
-	      && (loop_tree_node->reg_pressure[pclass]
-		  <= ira_class_hard_regs_num[pclass]))
+	  if ((flag_ira_region == IRA_REGION_MIXED
+	       && (loop_tree_node->reg_pressure[pclass]
+		   <= ira_class_hard_regs_num[pclass]))
+	      || regno == (int) REGNO (pic_offset_table_rtx))
 	    {
 	      if (! ALLOCNO_ASSIGNED_P (subloop_allocno))
 		{
Index: ira-emit.c
===================================================================
--- ira-emit.c	(revision 214576)
+++ ira-emit.c	(working copy)
@@ -620,7 +620,8 @@
 		  /* don't create copies because reload can spill an
 		     allocno set by copy although the allocno will not
 		     get memory slot.  */
-		  || ira_equiv_no_lvalue_p (regno)))
+		  || ira_equiv_no_lvalue_p (regno)
+		  || ALLOCNO_REGNO (allocno) == REGNO (pic_offset_table_rtx)))
 	    continue;
 	  original_reg = allocno_emit_reg (allocno);
 	  if (parent_allocno == NULL