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Re: Enable EBX for x86 in 32bits PIC code


On 08/28/14 02:37, Ilya Enkovich wrote:
2014-08-28 1:39 GMT+04:00 Jeff Law <law@redhat.com>:
On 08/26/14 15:42, Ilya Enkovich wrote:

diff --git a/gcc/calls.c b/gcc/calls.c
index 4285ec1..85dae6b 100644
--- a/gcc/calls.c
+++ b/gcc/calls.c
@@ -1122,6 +1122,14 @@ initialize_argument_information (int num_actuals
ATTRIBUTE_UNUSED,
       call_expr_arg_iterator iter;
       tree arg;

+    if (targetm.calls.implicit_pic_arg (fndecl ? fndecl : fntype))
+      {
+       gcc_assert (pic_offset_table_rtx);
+       args[j].tree_value = make_tree (ptr_type_node,
+                                       pic_offset_table_rtx);
+       j--;
+      }
+
       if (struct_value_addr_value)
         {
         args[j].tree_value = struct_value_addr_value;

So why do you need this?  Can't this be handled in the call/call_value
expanders or what about attaching the use to CALL_INSN_FUNCTION_USAGE from
inside ix86_expand_call?  Basically I'm not seeing the need for another
target hook here.  I think that would significantly simply the patch as
well.

GOT base address become an additional implicit arg with EBX relaxed
and I handled it as all other args. I can move EBX initialization into
ix86_expand_call. Would still need some hint from target to init
pic_offset_table_rtx with proper value in the beginning of function
expand.
It doesn't really need to be an argument in the traditional sense and adding it just complicates things with a target implementation detail as far as I can see.

I think you'll find that if you have the call pattern emit a copy from pic_offset_table_rtx into EBX and attach of use of EBX to the call then most of the code you've written to add the implicit argument just disappears.

jeff


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