[Patch, PR 57790] Waste work in can_move_insns_across()

[pchang9]

Hi,

The problem appears in revision 201034 in version 4.9.  I attached a
one-line patch that fixes it.  I also reported this problem
at http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57790

I bootstrapped and ran the regression tests for this patch on x86_64-linux
and all tests pass.

In method "can_move_insns_across()" in df-problems.c, the loop on line
4038 should break immediately after "fail" is set to 1. All the iterations
after "fail" set to 1 do not perform any useful work, at best they just
set "fail" again to 1.

Index: gcc/df-problems.c
===================================================================
--- gcc/df-problems.c   (revision 201034)
+++ gcc/df-problems.c   (working copy)
@@ -4040,7 +4040,10 @@
          if (i < FIRST_PSEUDO_REGISTER
              && ! fixed_regs[i]
              && ! global_regs[i])
-           fail = 1;
+           {
+             fail = 1;
+             break;
+           }
        }
     }


-Chang
Index: gcc/df-problems.c
===================================================================
--- gcc/df-problems.c   (revision 201034)
+++ gcc/df-problems.c   (working copy)
@@ -4040,7 +4040,10 @@
          if (i < FIRST_PSEUDO_REGISTER
              && ! fixed_regs[i]
              && ! global_regs[i])
-           fail = 1;
+           {
+             fail = 1;
+             break;
+           }
        }
     }