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The nvptx port [3/11+] Struct returns

Message ID 54451AB5.7040205@codesourcery.com
State New
Headers show

Commit Message

Bernd Schmidt Oct. 20, 2014, 2:22 p.m. UTC 
Even when returning a structure by passing an invisible reference, gcc 
still likes to set the return register to the address of the struct. 
This is undesirable on ptx where things like the return register have to 
be declared, and the function really returns void at ptx level. I've 
added a target hook to avoid this. I figure other targets might find it 
beneficial to omit this unnecessary set as well.


Bernd

Comments

Jeff Law Oct. 21, 2014, 6:36 p.m. UTC | #1 
On 10/20/14 14:22, Bernd Schmidt wrote:
> Even when returning a structure by passing an invisible reference, gcc
> still likes to set the return register to the address of the struct.
> This is undesirable on ptx where things like the return register have to
> be declared, and the function really returns void at ptx level. I've
> added a target hook to avoid this. I figure other targets might find it
> beneficial to omit this unnecessary set as well.
>
>
> Bernd
>
>
> 003-sretreg.diff
>
>
> 	gcc/
> 	* target.def (omit_struct_return_reg): New data hook.
> 	* doc/tm.texi.in: Add @hook TARGET_OMIT_STRUCT_RETURN_REG.
> 	* doc/tm.texi: Regenerate.
> 	* function.c (expand_function_end): Use it.
My first thought when reading this surprise that we actually return a 
value here and a desire to just zap that code completely since there's 
virtually no chance the optimizer will be able to delete it.

But then I remembered how much I hate dealing with this kind of ABI 
issue.  I suspect nobody actually specifies behavior here other than to 
indicate when pass by invisible reference is used and what register 
holds that incoming value.

Sooooo, OK for the trunk.

jeff
diff mbox

Patch

	gcc/
	* target.def (omit_struct_return_reg): New data hook.
	* doc/tm.texi.in: Add @hook TARGET_OMIT_STRUCT_RETURN_REG.
	* doc/tm.texi: Regenerate.
	* function.c (expand_function_end): Use it.

------------------------------------------------------------------------
Index: gcc/doc/tm.texi
===================================================================
--- gcc/doc/tm.texi	(revision 422355)
+++ gcc/doc/tm.texi	(revision 422356)
@@ -4560,6 +4560,14 @@  need more space than is implied by @code
 saving and restoring an arbitrary return value.
 @end defmac
 
+@deftypevr {Target Hook} bool TARGET_OMIT_STRUCT_RETURN_REG
+Normally, when a function returns a structure by memory, the address
+is passed as an invisible pointer argument, but the compiler also
+arranges to return the address from the function like it would a normal
+pointer return value.  Define this to true if that behaviour is
+undesirable on your target.
+@end deftypevr
+
 @deftypefn {Target Hook} bool TARGET_RETURN_IN_MSB (const_tree @var{type})
 This hook should return true if values of type @var{type} are returned
 at the most significant end of a register (in other words, if they are
Index: gcc/doc/tm.texi.in
===================================================================
--- gcc/doc/tm.texi.in	(revision 422355)
+++ gcc/doc/tm.texi.in	(revision 422356)
@@ -3769,6 +3769,8 @@  need more space than is implied by @code
 saving and restoring an arbitrary return value.
 @end defmac
 
+@hook TARGET_OMIT_STRUCT_RETURN_REG
+
 @hook TARGET_RETURN_IN_MSB
 
 @node Aggregate Return
Index: gcc/target.def
===================================================================
--- gcc/target.def	(revision 422355)
+++ gcc/target.def	(revision 422356)
@@ -3601,6 +3601,16 @@  structure value address at the beginning
 to emit adjusting code, you should do it at this point.",
  rtx, (tree fndecl, int incoming),
  hook_rtx_tree_int_null)
+
+DEFHOOKPOD
+(omit_struct_return_reg,
+ "Normally, when a function returns a structure by memory, the address\n\
+is passed as an invisible pointer argument, but the compiler also\n\
+arranges to return the address from the function like it would a normal\n\
+pointer return value.  Define this to true if that behaviour is\n\
+undesirable on your target.",
+ bool, false)
+
 DEFHOOK
 (return_in_memory,
  "This target hook should return a nonzero value to say to return the\n\
Index: gcc/function.c
===================================================================
--- gcc/function.c	(revision 422355)
+++ gcc/function.c	(revision 422356)
@@ -5179,8 +5179,8 @@  expand_function_end (void)
      If returning a structure PCC style,
      the caller also depends on this value.
      And cfun->returns_pcc_struct is not necessarily set.  */
-  if (cfun->returns_struct
-      || cfun->returns_pcc_struct)
+  if ((cfun->returns_struct || cfun->returns_pcc_struct)
+      && !targetm.calls.omit_struct_return_reg)
     {
       rtx value_address = DECL_RTL (DECL_RESULT (current_function_decl));
       tree type = TREE_TYPE (DECL_RESULT (current_function_decl));