[PR50869] don't attempt to expand CFA within cselib

[Alexandre Oliva <aoliva at redhat dot com>]

An assertion check meant to verify that var loc expansions that didn't
involve VALUEs (say constants, REGs, etc) didn't push values onto the
dependency stack failed in an expansion of the argp reg, because
equivalences for it are preserved at cselib table resets, and cselib
later tries to expand it to equivalent expressions.

It's not profitable to expand it within var-tracking, and that's the
only user of the CFA-base special-casing in cselib, so I arranged for
argp to be preserved in expansions, just like other stack base
registers.

While debugging it, I noticed it was theoretically possible for the
expression depth to remain uninitialized, and added an initialization
and an assertion check to make sure it only remains zero when no
location is found.

Regstrapped on x86_64-linux-gnu and i686-linux-gnu.  Ok to install?

for  gcc/ChangeLog
from  Alexandre Oliva  <aoliva@redhat.com>

	PR debug/50869
	* cselib.c (cfa_base_preserved_regno): Initialize.
	(cselib_expand_value_rtx_1): Don't expand it.
	* var-tracking.c (vt_expand_var_loc_chain): Initialize depth.
	Check it's only zero if result is NULL.

Index: gcc/cselib.c
===================================================================
--- gcc/cselib.c.orig	2011-10-27 18:32:20.137366314 -0200
+++ gcc/cselib.c	2011-10-27 18:27:05.387597000 -0200
@@ -185,7 +185,7 @@ static cselib_val dummy_val;
    that is constant through the whole function and should never be
    eliminated.  */
 static cselib_val *cfa_base_preserved_val;
-static unsigned int cfa_base_preserved_regno;
+static unsigned int cfa_base_preserved_regno = INVALID_REGNUM;
 
 /* Used to list all values that contain memory reference.
    May or may not contain the useless values - the list is compacted
@@ -1451,7 +1451,7 @@ cselib_expand_value_rtx_1 (rtx orig, str
 	  if (GET_MODE (l->elt->val_rtx) == GET_MODE (orig))
 	    {
 	      rtx result;
-	      int regno = REGNO (orig);
+	      unsigned regno = REGNO (orig);
 
 	      /* The only thing that we are not willing to do (this
 		 is requirement of dse and if others potential uses
@@ -1471,7 +1471,8 @@ cselib_expand_value_rtx_1 (rtx orig, str
 		 make the frame assumptions.  */
 	      if (regno == STACK_POINTER_REGNUM
 		  || regno == FRAME_POINTER_REGNUM
-		  || regno == HARD_FRAME_POINTER_REGNUM)
+		  || regno == HARD_FRAME_POINTER_REGNUM
+		  || regno == cfa_base_preserved_regno)
 		return orig;
 
 	      bitmap_set_bit (evd->regs_active, regno);
Index: gcc/var-tracking.c
===================================================================
--- gcc/var-tracking.c.orig	2011-10-27 18:32:20.141366261 -0200
+++ gcc/var-tracking.c	2011-10-27 18:28:03.823813000 -0200
@@ -7764,7 +7764,7 @@ vt_expand_var_loc_chain (variable var, b
   bool pending_recursion;
   rtx loc_from = NULL;
   struct elt_loc_list *cloc = NULL;
-  int depth, saved_depth = elcd->depth;
+  int depth = 0, saved_depth = elcd->depth;
 
   /* Clear all backlinks pointing at this, so that we're not notified
      while we're active.  */
@@ -7842,6 +7842,8 @@ vt_expand_var_loc_chain (variable var, b
   VAR_LOC_FROM (var) = loc_from;
   VAR_LOC_DEPTH (var) = depth;
 
+  gcc_checking_assert (!depth == !result);
+
   elcd->depth = update_depth (saved_depth, depth);
 
   /* Indicate whether any of the dependencies are pending recursion


-- 
Alexandre Oliva, freedom fighter    http://FSFLA.org/~lxoliva/
You must be the change you wish to see in the world. -- Gandhi
Be Free! -- http://FSFLA.org/   FSF Latin America board member
Free Software Evangelist      Red Hat Brazil Compiler Engineer