global.c (global_conflicts): Update comments.

        * global.c (global_conflicts): Update comments.
        (record_conflicts): No need to record conflicts between pseudos here.

From-SVN: r30492

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 4cedaf34bc75669e2b3ff873d17f855731b2b26d..9dcb970f537391f1d01a78936965f4f4b424433c 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+Thu Nov 11 18:54:24 1999  Jeffrey A Law  (law@cygnus.com)
+
+       * global.c (global_conflicts): Update comments.
+       (record_conflicts): No need to record conflicts between pseudos here.
+
 Thu Nov 11 12:42:11 MST 1999   Diego Novillo <dnovillo@cygnus.com>
 
        * gcc/cp/init.c (init_init_processing): Header information for

diff --git a/gcc/global.c b/gcc/global.c
index de3b57161e38459f75aed80d59e1054e03a03859..7e0074cbd63df7dafab03a0a524d835e16f08b85 100644 (file)
--- a/gcc/global.c
+++ b/gcc/global.c
@@ -673,7 +673,8 @@ global_conflicts ()
 
       /* Initialize table of registers currently live
         to the state at the beginning of this basic block.
-        This also marks the conflicts among them.
+        This also marks the conflicts among hard registers
+        and any allocnos that are live.
 
         For pseudo-regs, there is only one bit for each one
         no matter how many hard regs it occupies.
@@ -702,9 +703,30 @@ global_conflicts ()
                                         (a, PSEUDO_REGNO_MODE (i));
                                   });
 
-       /* Record that each allocno now live conflicts with each other
-          allocno now live, and with each hard reg now live.  */
+       /* Record that each allocno now live conflicts with each hard reg
+          now live.
 
+          It is not necessary to mark any conflicts between pseudos as
+          this point, even for pseudos which are live at the start of
+          the basic block.
+
+            Given two pseudos X and Y and any point in the CFG P.
+
+            On any path to point P where X and Y are live one of the
+            following conditions must be true:
+
+               1. X is live at some instruction on the path that
+                  evaluates Y.
+
+               2. Y is live at some instruction on the path that
+                  evaluates X.
+
+               3. Either X or Y is not evaluted on the path to P
+                  (ie it is used uninitialized) and thus the
+                  conflict can be ignored.
+
+           In cases #1 and #2 the conflict will be recorded when we
+           scan the instruction that makes either X or Y become live.  */
        record_conflicts (block_start_allocnos, ax);
 
 #ifdef STACK_REGS
@@ -1350,7 +1372,8 @@ record_one_conflict (regno)
 }
 
 /* Record all allocnos currently live as conflicting
-   with each other and with all hard regs currently live.
+   with all hard regs currently live.
+
    ALLOCNO_VEC is a vector of LEN allocnos, all allocnos that
    are currently live.  Their bits are also flagged in allocnos_live.  */
 
@@ -1368,8 +1391,6 @@ record_conflicts (allocno_vec, len)
       allocno = allocno_vec[len];
       ialloc_prod = allocno * allocno_row_words;
       IOR_HARD_REG_SET (hard_reg_conflicts[allocno], hard_regs_live);
-      for (j = allocno_row_words - 1; j >= 0; j--)
-       conflicts[ialloc_prod + j] |= allocnos_live[j];
     }
 }