can_implement_as_sibling_call_p REG_PARM_STACK_SPACE check

This moves an #ifdef block of code from calls.c to
targetm.function_ok_for_sibcall.  Only two targets, x86 and rs6000,
define REG_PARM_STACK_SPACE or OUTGOING_REG_PARM_STACK_SPACE macros
that might vary depending on the called function.  Macros like
UNITS_PER_WORD don't change over a function boundary, nor does the
MIPS ABI, nor does TARGET_64BIT on PA-RISC.  Other targets are even
more trivially proven to not need the calls.c code.

Besides cleaning up a small piece of #ifdef code, the motivation for
this patch is to allow tail calls on PowerPC for functions that
require less reg_parm_stack_space than their caller.  The original
code in calls.c only permitted tail calls when exactly equal, but on
PowerPC we can tail call if the callee has less or equal
REG_PARM_STACK_SPACE than the caller, as demonstrated by the
testcase.  So we should use

  /* If reg parm stack space increases, we cannot sibcall.  */
  if (REG_PARM_STACK_SPACE (decl ? decl : fntype)
      > INCOMING_REG_PARM_STACK_SPACE (current_function_decl))

and note the change to use INCOMING_REG_PARM_STACK_SPACE.
REG_PARM_STACK_SPACE has always been wrong there for PowerPC.  See
https://gcc.gnu.org/pipermail/gcc-patches/2014-May/389867.html for why
if you're curious.  Not that it matters, because PowerPC can do
without this check entirely, relying on a stack slot test in generic
code.

a) The generic code checks that arg passing stack in the callee is not
   greater than that in the caller, and,
b) ELFv2 only allocates reg_parm_stack_space when some parameter is
   passed on the stack.
Point (b) means that zero reg_parm_stack_space implies zero stack
space, and non-zero reg_parm_stack_space implies non-zero stack
space.  So the case of 0 reg_parm_stack_space in the caller and 64 in
the callee will be caught by (a).

gcc/
	PR middle-end/97267
	* calls.h (maybe_complain_about_tail_call): Declare.
	* calls.c (maybe_complain_about_tail_call): Make global.
	(can_implement_as_sibling_call_p): Delete reg_parm_stack_space
	param.  Adjust caller.  Move REG_PARM_STACK_SPACE check to..
	* config/i386/i386.c (ix86_function_ok_for_sibcall): ..here.

gcc/testsuite/
	PR middle-end/97267
	* gcc.target/powerpc/pr97267.c: New test.

1 files changed, 1 insertions, 17 deletions

diff --git a/gcc/calls.c b/gcc/calls.c
index a8f4596..1a7632d 100644
--- a/gcc/calls.c
+++ b/gcc/calls.c
@@ -1922,7 +1922,7 @@ maybe_warn_nonstring_arg (tree fndecl, tree exp)
 /* Issue an error if CALL_EXPR was flagged as requiring
    tall-call optimization.  */
 
-static void
+void
 maybe_complain_about_tail_call (tree call_expr, const char *reason)
 {
   gcc_assert (TREE_CODE (call_expr) == CALL_EXPR);
@@ -3525,7 +3525,6 @@ static bool
 can_implement_as_sibling_call_p (tree exp,
 				 rtx structure_value_addr,
 				 tree funtype,
-				 int reg_parm_stack_space ATTRIBUTE_UNUSED,
 				 tree fndecl,
 				 int flags,
 				 tree addr,
@@ -3550,20 +3549,6 @@ can_implement_as_sibling_call_p (tree exp,
       return false;
     }
 
-#ifdef REG_PARM_STACK_SPACE
-  /* If outgoing reg parm stack space changes, we cannot do sibcall.  */
-  if (OUTGOING_REG_PARM_STACK_SPACE (funtype)
-      != OUTGOING_REG_PARM_STACK_SPACE (TREE_TYPE (current_function_decl))
-      || (reg_parm_stack_space != REG_PARM_STACK_SPACE (current_function_decl)))
-    {
-      maybe_complain_about_tail_call (exp,
-				      "inconsistent size of stack space"
-				      " allocated for arguments which are"
-				      " passed in registers");
-      return false;
-    }
-#endif
-
   /* Check whether the target is able to optimize the call
      into a sibcall.  */
   if (!targetm.function_ok_for_sibcall (fndecl, exp))
@@ -4088,7 +4073,6 @@ expand_call (tree exp, rtx target, int ignore)
     try_tail_call = can_implement_as_sibling_call_p (exp,
 						     structure_value_addr,
 						     funtype,
-						     reg_parm_stack_space,
 						     fndecl,
 						     flags, addr, args_size);