[committed] Fix handling of global registers in MIPS prologues

[Richard Sandiford]

PR 45074 showed up a rather embarrassing oversight in the MIPS backend:
global registers were still being treated as call-saved.

Fixed with the attached patch.  Tested on mips64-linux-gnu and applied.

Richard


gcc/
        * config/mips/mips.c (mips_cfun_call_saved_reg_p): Handle global
        registers.

gcc/testsuite/
        * gcc.target/mips/reg-var-1.c: New test.

Index: gcc/config/mips/mips.c
===================================================================
--- gcc/config/mips/mips.c      2011-04-16 09:02:10.000000000 +0100
+++ gcc/config/mips/mips.c      2011-04-17 11:14:53.000000000 +0100
@@ -9097,6 +9097,11 @@ mips_interrupt_extra_call_saved_reg_p (u
 static bool
 mips_cfun_call_saved_reg_p (unsigned int regno)
 {
+  /* If the user makes an ordinarily-call-saved register global,
+     that register is no longer call-saved.  */
+  if (global_regs[regno])
+    return false;
+
   /* Interrupt handlers need to save extra registers.  */
   if (cfun->machine->interrupt_handler_p
       && mips_interrupt_extra_call_saved_reg_p (regno))
Index: gcc/testsuite/gcc.target/mips/reg-var-1.c
===================================================================
--- /dev/null   2011-04-17 10:56:28.045573347 +0100
+++ gcc/testsuite/gcc.target/mips/reg-var-1.c   2011-04-17 11:22:39.000000000 
+0100
@@ -0,0 +1,16 @@
+/* { dg-do run } */
+register int g asm ("$18");
+
+void __attribute__((noinline))
+test (void)
+{
+  g = g + 1;
+}
+
+int
+main (void)
+{
+  g = 2;
+  test ();
+  return g != 3;
+}