re PR rtl-optimization/42631 ("-fcompare-debug failure" with "-O1 -funroll-loops")

gcc/ChangeLog:
PR debug/42631
* web.c (union_defs): Add used argument, to combine uses of
uninitialized regs.
(entry_register): Adjust type and tests of used argument.
(web_main): Widen used for new use.  Pass it to union_defs.
* df.h (union_defs): Adjust prototype.
gcc/testsuite/ChangeLog:
PR debug/42631
* gcc.dg/pr42631.c: New.

From-SVN: r155765

5 files changed, 77 insertions, 30 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index b386622..ea2df0a 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,14 @@
 2010-01-09  Alexandre Oliva  <aoliva@redhat.com>
 
+	PR debug/42631
+	* web.c (union_defs): Add used argument, to combine uses of
+	uninitialized regs.
+	(entry_register): Adjust type and tests of used argument.
+	(web_main): Widen used for new use.  Pass it to union_defs.
+	* df.h (union_defs): Adjust prototype.
+
+2010-01-09  Alexandre Oliva  <aoliva@redhat.com>
+
 	PR debug/42630
 	* loop-unroll.c (referenced_in_one_insn_in_loop_p): Count debug
 	uses in new incoming argument.  Free body.
diff --git a/gcc/df.h b/gcc/df.h
index be37fa4..e1421d1 100644
--- a/gcc/df.h
+++ b/gcc/df.h
@@ -1115,8 +1115,8 @@ struct web_entry
 
 extern struct web_entry *unionfind_root (struct web_entry *);
 extern bool unionfind_union (struct web_entry *, struct web_entry *);
-extern void union_defs (df_ref,
-                        struct web_entry *, struct web_entry *,
+extern void union_defs (df_ref, struct web_entry *,
+			unsigned int *used, struct web_entry *,
 			bool (*fun) (struct web_entry *, struct web_entry *));
 
 #endif /* GCC_DF_H */
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index f9074e3..0b2c3a5 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,10 @@
 2010-01-09  Alexandre Oliva  <aoliva@redhat.com>
 
+	PR debug/42631
+	* gcc.dg/pr42631.c: New.
+
+2010-01-09  Alexandre Oliva  <aoliva@redhat.com>
+
 	PR debug/42630
 	* gcc.dg/pr42630.c: New.
 
diff --git a/gcc/testsuite/gcc.dg/pr42631.c b/gcc/testsuite/gcc.dg/pr42631.c
new file mode 100644
index 0000000..f5ac5a5
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr42631.c
@@ -0,0 +1,23 @@
+/* The function below expands to a loop whose latch block starts with
+   a PHI node and the corresponding debug stmt.  In RTL, there are no
+   PHI nodes, but the debug insn that references the incoming k
+   remains, even though one of the incoming edges has it
+   uninitialized.  After unrolling, however, the debug insn becomes
+   unconditional, and this exposed a problem in the webizer.  Because
+   DF doesn't combine the uses of an uninitialized pseudo into a
+   single UD chain, we created a separate web for each use.
+   Allocating separate registers or stack slots for each uninitialized
+   use is wasteful, but the problem became more apparent in
+   -fcompare-debug tests: register numbers went out of sync, and could
+   have caused codegen differences depending on whether or not the
+   debug insns were present.  The fix was to arrange for web to
+   combine uninitialized uses into a single web.  */
+
+/* { dg-do compile } */
+/* { dg-options "-g -O1 -funroll-loops -fcompare-debug" } */
+
+void foo()
+{
+  unsigned k;
+  while (--k > 0);
+}
diff --git a/gcc/web.c b/gcc/web.c
index 27e7f91..d562807 100644
--- a/gcc/web.c
+++ b/gcc/web.c
@@ -28,14 +28,6 @@ along with GCC; see the file COPYING3.  If not see
    is almost unusable.
 
    TODO
-    - Add code to keep debugging up-to-date after splitting user variable
-      pseudos.  This can be done by keeping track of all the pseudos used
-      for the variable and using life analysis information before reload
-      to determine which one is live and, in case more than one are live,
-      choose the one with the latest definition.
-
-      Other optimization passes can benefit from the infrastructure too.
-
     - We may use profile information and ignore infrequent use for the
       purpose of web unifying, inserting the compensation code later to
       implement full induction variable expansion for loops (currently
@@ -60,9 +52,6 @@ along with GCC; see the file COPYING3.  If not see
 #include "tree-pass.h"
 
 
-static rtx entry_register (struct web_entry *, df_ref, char *);
-static void replace_ref (df_ref, rtx);
-
 /* Find the root of unionfind tree (the representative of set).  */
 
 struct web_entry *
@@ -98,11 +87,16 @@ unionfind_union (struct web_entry *first, struct web_entry *second)
 
 /* For each use, all possible defs reaching it must come in the same
    register, union them.
-   FUN is the function that does the union.  */
+   FUN is the function that does the union.
+
+   In USED, we keep the DF_REF_ID of the first uninitialized uses of a
+   register, so that all uninitialized uses of the register can be
+   combined into a single web.  We actually offset it by 2, because
+   the values 0 and 1 are reserved for use by entry_register.  */
 
 void
 union_defs (df_ref use, struct web_entry *def_entry,
- 	    struct web_entry *use_entry,
+	    unsigned int *used, struct web_entry *use_entry,
  	    bool (*fun) (struct web_entry *, struct web_entry *))
 {
   struct df_insn_info *insn_info = DF_REF_INSN_INFO (use);
@@ -169,6 +163,25 @@ union_defs (df_ref use, struct web_entry *def_entry,
 	    def_link++;
 	  }
     }
+
+  /* UD chains of uninitialized REGs are empty.  Keeping all uses of
+     the same uninitialized REG in a single web is not necessary for
+     correctness, since the uses are undefined, but it's wasteful to
+     allocate one register or slot for each reference.  Furthermore,
+     creating new pseudos for uninitialized references in debug insns
+     (see PR 42631) causes -fcompare-debug failures.  We record the
+     number of the first uninitialized reference we found, and merge
+     with it any other uninitialized references to the same
+     register.  */
+  if (!link)
+    {
+      int regno = REGNO (DF_REF_REAL_REG (use));
+      if (used[regno])
+	(*fun) (use_entry + DF_REF_ID (use), use_entry + used[regno] - 2);
+      else
+	used[regno] = DF_REF_ID (use) + 2;
+    }
+
   while (link)
     {
       (*fun) (use_entry + DF_REF_ID (use),
@@ -201,7 +214,7 @@ union_defs (df_ref use, struct web_entry *def_entry,
 /* Find the corresponding register for the given entry.  */
 
 static rtx
-entry_register (struct web_entry *entry, df_ref ref, char *used)
+entry_register (struct web_entry *entry, df_ref ref, unsigned int *used)
 {
   struct web_entry *root;
   rtx reg, newreg;
@@ -214,17 +227,14 @@ entry_register (struct web_entry *entry, df_ref ref, char *used)
   /* We are seeing this web for the first time, do the assignment.  */
   reg = DF_REF_REAL_REG (ref);
 
-  /* In case the original register is already assigned, generate new one.  */
-  if (!used[REGNO (reg)])
+  /* In case the original register is already assigned, generate new
+     one.  Since we use USED to merge uninitialized refs into a single
+     web, we might found an element to be nonzero without our having
+     used it.  Test for 1, because union_defs saves it for our use,
+     and there won't be any use for the other values when we get to
+     this point.  */
+  if (used[REGNO (reg)] != 1)
     newreg = reg, used[REGNO (reg)] = 1;
-  else if (REG_USERVAR_P (reg) && 0/*&& !flag_messy_debugging*/)
-    {
-      newreg = reg;
-      if (dump_file)
-	fprintf (dump_file,
-		 "New web forced to keep reg=%i (user variable)\n",
-		 REGNO (reg));
-    }
   else
     {
       newreg = gen_reg_rtx (GET_MODE (reg));
@@ -273,7 +283,7 @@ web_main (void)
   struct web_entry *def_entry;
   struct web_entry *use_entry;
   unsigned int max = max_reg_num ();
-  char *used;
+  unsigned int *used;
   basic_block bb;
   unsigned int uses_num = 0;
   rtx insn;
@@ -308,7 +318,7 @@ web_main (void)
 
   /* Record the number of uses and defs at the beginning of the optimization.  */
   def_entry = XCNEWVEC (struct web_entry, DF_DEFS_TABLE_SIZE());
-  used = XCNEWVEC (char, max);
+  used = XCNEWVEC (unsigned, max);
   use_entry = XCNEWVEC (struct web_entry, uses_num);
 
   /* Produce the web.  */
@@ -323,13 +333,13 @@ web_main (void)
 	    {
 	      df_ref use = *use_rec;
 	      if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)
-		union_defs (use, def_entry, use_entry, unionfind_union);
+		union_defs (use, def_entry, used, use_entry, unionfind_union);
 	    }
 	  for (use_rec = DF_INSN_UID_EQ_USES (uid); *use_rec; use_rec++)
 	    {
 	      df_ref use = *use_rec;
 	      if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER)
-		union_defs (use, def_entry, use_entry, unionfind_union);
+		union_defs (use, def_entry, used, use_entry, unionfind_union);
 	    }
 	}
     }