Fix indirect sibcall check for MIPS16 functions

[Richard Sandiford]

MIPS doesn't allow direct sibcalls to MIPS16 functions, because there's
no direct jump instruction that swaps the ISA mode.  The check for this
case would segfault for indirect calls, where no decl is available.

Tested on mipsisa64-elfoabi and applied.  The testcase is
r10k-cache-barrier-13.c

Richard


gcc/
	* config/mips/mips.c (mips_function_ok_for_sibcall): Check for
	DECL being null.

Index: gcc/config/mips/mips.c
===================================================================
--- gcc/config/mips/mips.c	2008-09-06 10:10:24.000000000 +0100
+++ gcc/config/mips/mips.c	2008-09-06 10:10:30.000000000 +0100
@@ -6173,7 +6173,8 @@ mips_function_ok_for_sibcall (tree decl,
      because there is no direct "jx" instruction equivalent to "jalx" to
      switch the ISA mode.  We only care about cases where the sibling
      and normal calls would both be direct.  */
-  if (mips_use_mips16_mode_p (decl)
+  if (decl
+      && mips_use_mips16_mode_p (decl)
       && const_call_insn_operand (XEXP (DECL_RTL (decl), 0), VOIDmode))
     return false;