[backport gcc-4.7/trunk r172616 to fix PR target/43700 on MIPS <mikpe@it.uu.se>]

gcc/

2011-04-17  Richard Sandiford  <rdsandiford@googlemail.com>

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

gcc/testsuite/

2011-04-17  Richard Sandiford  <rdsandiford@googlemail.com>

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

--- gcc-4.6.0/gcc/config/mips/mips.c.~1~	2011-03-08 21:51:11.000000000 +0100
+++ gcc-4.6.0/gcc/config/mips/mips.c	2011-04-17 21:28:06.000000000 +0200
@@ -9053,6 +9053,11 @@ 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))
--- gcc-4.6.0/gcc/testsuite/gcc.target/mips/reg-var-1.c.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.6.0/gcc/testsuite/gcc.target/mips/reg-var-1.c	2011-04-17 21:28:06.000000000 +0200
@@ -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;
+}