Re: [patch] Fix var-tracking with dynamic stack realignment on x86

[Eric Botcazou <ebotcazou at adacore dot com>]

> I think re-test is just waste of cycles, as you know cfa_base_rtx is
> arg_pointer_rtx on both x86_64 and i686 (it is frame_pointer_rtx only on
> pa, vax and rx).  IMHO just testing if var-tracking still compiles without
> warnings ought to be enough.

Alright, quickstrapped and guality-regtested only.  Note that I tweaked the 
test as it didn't FAIL for me (it was UNSUPPORTED on i586 because of a "cannot 
access memory" error from within GDB and PASSed on x86-64).

Thanks for your help.


2011-05-30  Jakub Jelinek  <jakub@redhat.com>
            Eric Botcazou  <ebotcazou@adacore.com>

        * var-tracking.c (vt_add_function_parameter): Remap incoming MEMs with
        crtl->args.internal_arg_pointer based address to arg_pointer_rtx if
        there is a DRAP register and arg_pointer_rtx is the CFA pointer.
        (vt_init_cfa_base): Don't equate cfa_base_rtx if stack was realigned.
        (vt_initialize): Initialize cfa_base_rtx if there is a DRAP register.


2011-05-30  Jakub Jelinek  <jakub@redhat.com>
            Eric Botcazou  <ebotcazou@adacore.com>

	* gcc.dg/guality/drap.c: New test.


-- 
Eric Botcazou

Index: var-tracking.c
===================================================================
--- var-tracking.c	(revision 174377)
+++ var-tracking.c	(working copy)
@@ -8398,6 +8398,28 @@ vt_add_function_parameter (tree parm)
   if (GET_MODE (decl_rtl) == BLKmode || GET_MODE (incoming) == BLKmode)
     return;
 
+  /* If there is a DRAP register, rewrite the incoming location of parameters
+     passed on the stack into MEMs based on the argument pointer, as the DRAP
+     register can be reused for other purposes and we do not track locations
+     based on generic registers.  But the prerequisite is that this argument
+     pointer be also the virtual CFA pointer, see vt_initialize.  */
+  if (MEM_P (incoming)
+      && stack_realign_drap
+      && arg_pointer_rtx == cfa_base_rtx
+      && (XEXP (incoming, 0) == crtl->args.internal_arg_pointer
+	  || (GET_CODE (XEXP (incoming, 0)) == PLUS
+	      && XEXP (XEXP (incoming, 0), 0)
+		 == crtl->args.internal_arg_pointer
+	      && CONST_INT_P (XEXP (XEXP (incoming, 0), 1)))))
+    {
+      HOST_WIDE_INT off = -FIRST_PARM_OFFSET (current_function_decl);
+      if (GET_CODE (XEXP (incoming, 0)) == PLUS)
+	off += INTVAL (XEXP (XEXP (incoming, 0), 1));
+      incoming
+	= replace_equiv_address_nv (incoming,
+				    plus_constant (arg_pointer_rtx, off));
+    }
+
   if (!vt_get_decl_and_offset (incoming, &decl, &offset))
     {
       if (REG_P (incoming) || MEM_P (incoming))
@@ -8647,9 +8669,11 @@ vt_init_cfa_base (void)
 
   /* Tell alias analysis that cfa_base_rtx should share
      find_base_term value with stack pointer or hard frame pointer.  */
-  vt_equate_reg_base_value (cfa_base_rtx,
-			    frame_pointer_needed
-			    ? hard_frame_pointer_rtx : stack_pointer_rtx);
+  if (!frame_pointer_needed)
+    vt_equate_reg_base_value (cfa_base_rtx, stack_pointer_rtx);
+  else if (!crtl->stack_realign_tried)
+    vt_equate_reg_base_value (cfa_base_rtx, hard_frame_pointer_rtx);
+
   val = cselib_lookup_from_insn (cfa_base_rtx, GET_MODE (cfa_base_rtx), 1,
 				 VOIDmode, get_insns ());
   preserve_value (val);
@@ -8780,6 +8804,33 @@ vt_initialize (void)
 	fp_cfa_offset = -1;
     }
 
+  /* If the stack is realigned and a DRAP register is used, we're going to
+     rewrite MEMs based on it representing incoming locations of parameters
+     passed on the stack into MEMs based on the argument pointer.  Although
+     we aren't going to rewrite other MEMs, we still need to initialize the
+     virtual CFA pointer in order to ensure that the argument pointer will
+     be seen as a constant throughout the function.
+
+     ??? This doesn't work if FRAME_POINTER_CFA_OFFSET is defined.  */
+  else if (stack_realign_drap)
+    {
+      rtx reg, elim;
+
+#ifdef FRAME_POINTER_CFA_OFFSET
+      reg = frame_pointer_rtx;
+#else
+      reg = arg_pointer_rtx;
+#endif
+      elim = eliminate_regs (reg, VOIDmode, NULL_RTX);
+      if (elim != reg)
+	{
+	  if (GET_CODE (elim) == PLUS)
+	    elim = XEXP (elim, 0);
+	  if (elim == hard_frame_pointer_rtx)
+	    vt_init_cfa_base ();
+	}
+    }
+
   if (frame_pointer_needed)
     {
       rtx insn;

/* { dg-do run { target { i?86-*-* x86_64-*-* } } } */
/* { dg-options "-g -mforce-drap" } */

volatile int v;

__attribute__((noinline, noclone)) int
bar (int a, int b)
{
#ifdef __x86_64__
  asm volatile ("movq %%rsp, %%r10" : : : "r10");
#else
  asm volatile ("movl %%esp, %%ecx" : : : "ecx");
#endif
  return 0;
}

__attribute__((noinline, noclone)) int
foo (int v0, int v1, int v2, int v3, int v4, int v5, int a, int b)
{
  __attribute__((aligned (32))) int c = bar (a, b);
  v++;               /* { dg-final { gdb-test 21 "a" "5" } } */
  return a + b + c;  /* { dg-final { gdb-test 22 "b" "6" } } */
}

int
main (void)
{
  foo (0, 0, 0, 0, 0, 0, 5, 6);
  return 0;
}