[PATCH, SPU] Fix PR47179 (Re: [PATCH] Prepare for a fix for PR47179)

[Ulrich Weigand]

Richard Guenther wrote:

> This makes it possible to specify a target specific way to disambiguate
> against errno.  SPU has a particular bad way that isn't caught by
> the generic implementation (and I'll leave it to the target maintainer
> to implement one, the most trivial one just returning true always).

Thanks!  Using this patch and the one below fixes the test case on SPU.

Before I commit the SPU patch, I was wondering if you had any hints or
suggestions how to tighten up the check.  Since our errno is part of
a structure, we actually have to mark the whole *structure* as aliased
with errno.  Thus the patch currently simply considers *any* global
external variable of structure type to potentially alias errno.

Should this maybe tightened down to just structure types that contain
an "int"?  Maybe even just those with an "int" as first member?  It
would probably not be a good idea to actually check for the specific
struct tag name ...

On the other hand, it might not be really critical either way.


Patch tested on spu-elf with no regression.

Bye,
Ulrich

ChangeLog:

	PR tree-optimization/47179
	* config/spu/spu.c (spu_ref_may_alias_errno): New function.
	(TARGET_REF_MAY_ALIAS_ERRNO): Define.


Index: gcc/config/spu/spu.c
===================================================================
*** gcc/config/spu/spu.c	(revision 168909)
--- gcc/config/spu/spu.c	(working copy)
*************** static void spu_unique_section (tree, in
*** 230,235 ****
--- 230,236 ----
  static rtx spu_expand_load (rtx, rtx, rtx, int);
  static void spu_trampoline_init (rtx, tree, rtx);
  static void spu_conditional_register_usage (void);
+ static bool spu_ref_may_alias_errno (ao_ref *);
  
  /* Which instruction set architecture to use.  */
  int spu_arch;
*************** static const struct attribute_spec spu_a
*** 491,496 ****
--- 492,500 ----
  #undef TARGET_CONDITIONAL_REGISTER_USAGE
  #define TARGET_CONDITIONAL_REGISTER_USAGE spu_conditional_register_usage
  
+ #undef TARGET_REF_MAY_ALIAS_ERRNO
+ #define TARGET_REF_MAY_ALIAS_ERRNO spu_ref_may_alias_errno
+ 
  struct gcc_target targetm = TARGET_INITIALIZER;
  
  static void
*************** spu_function_profiler (FILE * file, int 
*** 7150,7153 ****
--- 7154,7179 ----
    fprintf (file, "brsl $75,  _mcount\n");
  }
  
+ /* Implement targetm.ref_may_alias_errno.  */
+ static bool
+ spu_ref_may_alias_errno (ao_ref *ref)
+ {
+   tree base = ao_ref_base (ref);
+ 
+   /* With SPU newlib, errno is defined as something like
+          _impure_data._errno
+      The default implementation of this target macro does not
+      recognize such expressions.
+ 
+      To fix this, we assume here that any access to a global variable
+      of structure type may alias errno.  */
+ 
+   if (DECL_P (base)
+       && !TREE_STATIC (base)
+       && TREE_CODE (TREE_TYPE (base)) == RECORD_TYPE)
+     return true;
+ 
+   return default_ref_may_alias_errno (ref);
+ }
+ 
  #include "gt-spu.h"
-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com