[Patch, IRA] Fix a function accessing beyond end-of-array

[Hari Sandanagobalane]

Hello,
I discussed this problem with Vlad in 
http://gcc.gnu.org/ml/gcc/2011-05/msg00131.html. I propose the following 
patch to fix it. Okay to commit?

Revised the ChangeLog.

Thanks
Hari

ChangeLog:
        * ira.c (clarify_prohibited_class_mode_regs): Prevent the 
function from accessing beyond the end of REGNO_REG_CLASS array by 
stopping the loop early.

Patch:
Index: gcc/ira.c
===================================================================
--- gcc/ira.c   (revision 173654)
+++ gcc/ira.c   (working copy)
@@ -1422,6 +1422,12 @@
           if (TEST_HARD_REG_BIT 
(ira_prohibited_class_mode_regs[cl][j], hard_regno))
             continue;
           nregs = hard_regno_nregs[hard_regno][j];
+          if (hard_regno + nregs >= FIRST_PSEUDO_REGISTER)
+            {
+              SET_HARD_REG_BIT (ira_prohibited_class_mode_regs[cl][j],
+                                hard_regno);
+               continue;
+            }
           pclass = ira_pressure_class_translate[REGNO_REG_CLASS 
(hard_regno)];
           for (nregs-- ;nregs >= 0; nregs--)
             if (((enum reg_class) pclass