(schedule_insns): Don't zero reg_n_calls_crossed for

pseudos live across multiple blocks.

From-SVN: r5515

diff --git a/gcc/sched.c b/gcc/sched.c
index b067d36abaa6c0396967670347d2ecd22ab09e7a..a56aa47cd2e0b4e924a252d762a568acaf72cf19 100644 (file)
--- a/gcc/sched.c
+++ b/gcc/sched.c
@@ -4678,20 +4678,38 @@ schedule_insns (dump_file)
                           regno, reg_live_length[regno],
                           sched_reg_live_length[regno]);
 
-               if (reg_n_calls_crossed[regno]
-                   && ! sched_reg_n_calls_crossed[regno])
-                 fprintf (dump_file,
-                          ";; register %d no longer crosses calls\n", regno);
-               else if (! reg_n_calls_crossed[regno]
-                        && sched_reg_n_calls_crossed[regno])
+               if (! reg_n_calls_crossed[regno]
+                   && sched_reg_n_calls_crossed[regno])
                  fprintf (dump_file,
                           ";; register %d now crosses calls\n", regno);
+               else if (reg_n_calls_crossed[regno]
+                        && ! sched_reg_n_calls_crossed[regno]
+                        && reg_basic_block[regno] != REG_BLOCK_GLOBAL)
+                 fprintf (dump_file,
+                          ";; register %d no longer crosses calls\n", regno);
+
              }
            /* Negative values are special; don't overwrite the current
               reg_live_length value if it is negative.  */
            if (reg_live_length[regno] >= 0)
              reg_live_length[regno] = sched_reg_live_length[regno];
-           reg_n_calls_crossed[regno] = sched_reg_n_calls_crossed[regno];
+
+           /* We can't change the value of reg_n_calls_crossed to zero for
+              pseudos which are live in more than one block.
+
+              This is because combine might have made an optimization which
+              invalidated basic_block_live_at_start and reg_n_calls_crossed,
+              but it does not update them.  If we update reg_n_calls_crossed
+              here, the two variables are now inconsistent, and this might
+              confuse the caller-save code into saving a register that doesn't
+              need to be saved.  This is only a problem when we zero calls
+              crossed for a pseudo live in multiple basic blocks.
+
+              Alternatively, we could try to correctly update basic block live
+              at start here in sched, but that seems complicated.  */
+           if (sched_reg_n_calls_crossed[regno]
+               || reg_basic_block[regno] != REG_BLOCK_GLOBAL)
+             reg_n_calls_crossed[regno] = sched_reg_n_calls_crossed[regno];
          }
     }
 }