re PR rtl-optimization/8967 (Making class data members `const' pessimizes code)

	PR optimization/8967
	* alias.c (write_dependence_p): Modify to take an additional constp
	argument that controls whether the UNCHANGING_RTX_P flags are used.
	(anti_dependence, output_dependence): Adjust write_dependence_p
	callers to pass this additional argument, to return the same result.
	(unchanging_anti_dependence): New variant of anti_dependence that
	ignores the UNCHANGING_RTX_P property on memory references.
	* rtl.h (unchaning_anti_dependence): Prototype here.
	* flow.c (init_propagate_block): Place fake constant mem writes on
	the mem_set_list so that dead writes to const variables are deleted.
	(insn_dead_p): Change anti_dependence to unchanging_anti_dependence.
	(mark_used_regs): Likewise.

From-SVN: r71332

gcc/ChangeLog

+2003-09-12  Roger Sayle  <roger@eyesopen.com>
+
+	PR optimization/8967
+	* alias.c (write_dependence_p): Modify to take an additional constp
+	argument that controls whether the UNCHANGING_RTX_P flags are used.
+	(anti_dependence, output_dependence): Adjust write_dependence_p
+	callers to pass this additional argument, to return the same result.
+	(unchanging_anti_dependence): New variant of anti_dependence that
+	ignores the UNCHANGING_RTX_P property on memory references.
+	* rtl.h (unchaning_anti_dependence): Prototype here.
+	* flow.c (init_propagate_block): Place fake constant mem writes on
+	the mem_set_list so that dead writes to const variables are deleted.
+	(insn_dead_p): Change anti_dependence to unchanging_anti_dependence.
+	(mark_used_regs): Likewise.
+
 2003-09-12  Richard Sandiford  <rsandifo@redhat.com>
 
 	* config/mcore/mcore-protos.h (mcore_r15_operand_p): Declare.

gcc/alias.c

@@ -110,7 +110,7 @@ static bool nonoverlapping_component_refs_p (tree, tree);
 static tree decl_for_component_ref (tree);
 static rtx adjust_offset_for_component_ref (tree, rtx);
 static int nonoverlapping_memrefs_p (rtx, rtx);
-static int write_dependence_p (rtx, rtx, int);
+static int write_dependence_p (rtx, rtx, int, int);
 
 static int nonlocal_mentioned_p_1 (rtx *, void *);
 static int nonlocal_mentioned_p (rtx);
@@ -2202,10 +2202,11 @@ canon_true_dependence (rtx mem, enum machine_mode mem_mode, rtx mem_addr,
 }
 
 /* Returns nonzero if a write to X might alias a previous read from
-   (or, if WRITEP is nonzero, a write to) MEM.  */
+   (or, if WRITEP is nonzero, a write to) MEM.  If CONSTP is non-zero,
+   honor the RTX_UNCHANGING_P flags on X and MEM.  */
 
 static int
-write_dependence_p (rtx mem, rtx x, int writep)
+write_dependence_p (rtx mem, rtx x, int writep, int constp)
 {
   rtx x_addr, mem_addr;
   rtx fixed_scalar;
@@ -2224,15 +2225,18 @@ write_dependence_p (rtx mem, rtx x, int writep)
   if (DIFFERENT_ALIAS_SETS_P (x, mem))
     return 0;
 
-  /* Unchanging memory can't conflict with non-unchanging memory.  */
-  if (RTX_UNCHANGING_P (x) != RTX_UNCHANGING_P (mem))
-    return 0;
+  if (constp)
+    {
+      /* Unchanging memory can't conflict with non-unchanging memory.  */
+      if (RTX_UNCHANGING_P (x) != RTX_UNCHANGING_P (mem))
+	return 0;
 
-  /* If MEM is an unchanging read, then it can't possibly conflict with
-     the store to X, because there is at most one store to MEM, and it must
-     have occurred somewhere before MEM.  */
-  if (! writep && RTX_UNCHANGING_P (mem))
-    return 0;
+      /* If MEM is an unchanging read, then it can't possibly conflict with
+	 the store to X, because there is at most one store to MEM, and it
+	 must have occurred somewhere before MEM.  */
+      if (! writep && RTX_UNCHANGING_P (mem))
+	return 0;
+    }
 
   if (nonoverlapping_memrefs_p (x, mem))
     return 0;
@@ -2273,7 +2277,7 @@ write_dependence_p (rtx mem, rtx x, int writep)
 int
 anti_dependence (rtx mem, rtx x)
 {
-  return write_dependence_p (mem, x, /*writep=*/0);
+  return write_dependence_p (mem, x, /*writep=*/0, /*constp*/1);
 }
 
 /* Output dependence: X is written after store in MEM takes place.  */
@@ -2281,7 +2285,16 @@ anti_dependence (rtx mem, rtx x)
 int
 output_dependence (rtx mem, rtx x)
 {
-  return write_dependence_p (mem, x, /*writep=*/1);
+  return write_dependence_p (mem, x, /*writep=*/1, /*constp*/1);
+}
+
+/* Unchanging anti dependence: Like anti_dependence but ignores
+   the UNCHANGING_RTX_P property on const variable references.  */
+
+int
+unchanging_anti_dependence (rtx mem, rtx x)
+{
+  return write_dependence_p (mem, x, /*writep=*/0, /*constp*/0);
 }
 
 /* A subroutine of nonlocal_mentioned_p, returns 1 if *LOC mentions

gcc/flow.c

@@ -1974,13 +1974,6 @@ init_propagate_block_info (basic_block bb, regset live, regset local_set,
 	    rtx mem = SET_DEST (set);
 	    rtx canon_mem = canon_rtx (mem);
 
-	    /* This optimization is performed by faking a store to the
-	       memory at the end of the block.  This doesn't work for
-	       unchanging memories because multiple stores to unchanging
-	       memory is illegal and alias analysis doesn't consider it.  */
-	    if (RTX_UNCHANGING_P (canon_mem))
-	      continue;
-
 	    if (XEXP (canon_mem, 0) == frame_pointer_rtx
 		|| (GET_CODE (XEXP (canon_mem, 0)) == PLUS
 		    && XEXP (XEXP (canon_mem, 0), 0) == frame_pointer_rtx
@@ -2152,7 +2145,7 @@ insn_dead_p (struct propagate_block_info *pbi, rtx x, int call_ok,
 	     rtx_equal_p does not check the alias set or flags, we also
 	     must have the potential for them to conflict (anti_dependence).  */
 	  for (temp = pbi->mem_set_list; temp != 0; temp = XEXP (temp, 1))
-	    if (anti_dependence (r, XEXP (temp, 0)))
+	    if (unchanging_anti_dependence (r, XEXP (temp, 0)))
 	      {
 		rtx mem = XEXP (temp, 0);
 
@@ -3730,7 +3723,7 @@ mark_used_regs (struct propagate_block_info *pbi, rtx x, rtx cond, rtx insn)
 	      while (temp)
 		{
 		  next = XEXP (temp, 1);
-		  if (anti_dependence (XEXP (temp, 0), x))
+		  if (unchanging_anti_dependence (XEXP (temp, 0), x))
 		    {
 		      /* Splice temp out of the list.  */
 		      if (prev)

gcc/rtl.h

@@ -2253,6 +2253,7 @@ extern int canon_true_dependence (rtx, enum machine_mode, rtx, rtx,
 extern int read_dependence (rtx, rtx);
 extern int anti_dependence (rtx, rtx);
 extern int output_dependence (rtx, rtx);
+extern int unchanging_anti_dependence (rtx, rtx);
 extern void mark_constant_function (void);
 extern void init_alias_once (void);
 extern void init_alias_analysis (void);