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[rfc] Expose more tailcall opportunities (PR
- From: Steven Bosscher <stevenb at suse dot de>
- To: gcc-patches at gcc dot gnu dot org
- Cc: rth at redhat dot com
- Date: Wed, 20 Jul 2005 01:26:29 +0200
- Subject: [rfc] Expose more tailcall opportunities (PR
Hi,
Rth had this nice example some time ago:
struct S { int w, x, y, z; };
struct T { int r; struct S s; };
void bar (struct S, int);
void foo (int a, struct T b)
{
struct S *c = 0;
if (a)
c = &b.s;
bar (*c, a);
}
GCC currently doesn't produce a tail call for this, but it could.
With the attached patch, tree-tailcall can see that even though
b is addressable, b is not call clobbered. That means, iiuc, that
its address doesn't escape either. Does this patch make sense?
It passed bootstrap and testing on x86_64 (unix{,-m32}) and on ppc.
Gr.
Steven
Index: tree-tailcall.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/tree-tailcall.c,v
retrieving revision 2.45
diff -u -3 -p -r2.45 tree-tailcall.c
--- tree-tailcall.c 13 Jul 2005 22:35:28 -0000 2.45
+++ tree-tailcall.c 18 Jul 2005 09:21:02 -0000
@@ -185,7 +185,7 @@ suitable_for_tail_call_opt_p (void)
for (param = DECL_ARGUMENTS (current_function_decl);
param;
param = TREE_CHAIN (param))
- if (TREE_ADDRESSABLE (param))
+ if (TREE_ADDRESSABLE (param) && is_call_clobbered (param))
return false;
return true;