[RS6000] ABI_V4 init of toc section

[Alan Modra <amodra at gmail dot com>]

Since 4c4a180d, LTO has turned off flag_pic when linking a fixed
position executable.  This results in flag_pic being zero in
rs6000_file_start, and no definition of ".LCTOC1".

However, when we get to actually emitting code, flag_pic may be on
again, and references made to ".LCTOC1".  How flag_pic comes to be
enabled again is quite a story.  It goes like this..  If a function is
compiled with -fPIC then sysv4.h SUBTARGET_OVERRIDE_OPTIONS will set
TARGET_RELOCATABLE.  Conversely, if TARGET_RELOCATABLE is set and
flag_pic is zero, then SUBTARGET_OVERRIDE_OPTIONS will set flag_pic=2.
It also happens that TARGET_RELOCATABLE is a bit in rs6000_isa_flags,
which is handled by rs6000_function_specific_save and
rs6000_function_specific_restore.  That last fact means lto streaming
keeps track of the state of TARGET_RELOCATABLE for functions, and when
options are restored for a given function we'll set flag_pic=2 if the
function was originally compiled with -fPIC.  That's bad because it
defeats the purpose of the 4c4a180d lto change, resulting in worse
optimization of ppc32 executables.  What's more, we don't seem to turn
off flag_pic once it is on.

We should really untangle the flag_pic/TARGET_RELOCATABLE mess, but
that change is probably a little dangerous for stage4.  Instead, this
patch removes the toc symbol initialization from file_start and does
so when the first item is emitted to the toc, or after the function
epilogue in the cases where we emit code to initialize a toc pointer
but don't actually use it (-O0 mostly, I think).

Bootstrapped and regression tested powerpc64-linux biarch with all
languages enabled.  OK to apply?

	PR target/68662
	* config/rs6000/rs6000.c (need_toc_init): New var, set it
	whenever toc_label_name used.
	(rs6000_file_start): Don't set up toc section here,
	(rs6000_output_function_epilogue): do so here instead,
	(rs6000_xcoff_file_start): and here.
	* config/rs6000/rs6000.md (load_toc_aix_si): Set need_toc_init.
	(load_toc_aix_di): Likewise.

diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index 4704d00..4ea4efb 100644
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -209,7 +209,7 @@ tree rs6000_builtin_types[RS6000_BTI_MAX];
 tree rs6000_builtin_decls[RS6000_BUILTIN_COUNT];
 
 /* Flag to say the TOC is initialized */
-int toc_initialized;
+int toc_initialized, need_toc_init;
 char toc_label_name[10];
 
 /* Cached value of rs6000_variable_issue. This is cached in
@@ -5682,13 +5682,6 @@ rs6000_file_start (void)
 
   if (DEFAULT_ABI == ABI_ELFv2)
     fprintf (file, "\t.abiversion 2\n");
-
-  if (DEFAULT_ABI == ABI_AIX || DEFAULT_ABI == ABI_ELFv2
-      || (TARGET_ELF && flag_pic == 2))
-    {
-      switch_to_section (toc_section);
-      switch_to_section (text_section);
-    }
 }
 
 
@@ -20375,6 +20368,7 @@ rs6000_output_addr_const_extra (FILE *file, rtx x)
 	  {
 	    putc ('-', file);
 	    assemble_name (file, toc_label_name);
+	    need_toc_init = 1;
 	  }
 	else if (TARGET_ELF)
 	  fputs ("@toc", file);
@@ -24003,7 +23997,10 @@ rs6000_emit_load_toc_table (int fromprolog)
       ASM_GENERATE_INTERNAL_LABEL (buf, "L", CODE_LABEL_NUMBER (lab));
       lab = gen_rtx_SYMBOL_REF (Pmode, ggc_strdup (buf));
       if (flag_pic == 2)
-	got = gen_rtx_SYMBOL_REF (Pmode, ggc_strdup (toc_label_name));
+	{
+	  got = gen_rtx_SYMBOL_REF (Pmode, ggc_strdup (toc_label_name));
+	  need_toc_init = 1;
+	}
       else
 	got = rs6000_got_sym ();
       tmp1 = tmp2 = dest;
@@ -24048,6 +24045,7 @@ rs6000_emit_load_toc_table (int fromprolog)
 	  rtx tocsym, lab;
 
 	  tocsym = gen_rtx_SYMBOL_REF (Pmode, ggc_strdup (toc_label_name));
+	  need_toc_init = 1;
 	  lab = gen_label_rtx ();
 	  emit_insn (gen_load_toc_v4_PIC_1b (tocsym, lab));
 	  emit_move_insn (dest, gen_rtx_REG (Pmode, LR_REGNO));
@@ -24062,6 +24060,7 @@ rs6000_emit_load_toc_table (int fromprolog)
       /* This is for AIX code running in non-PIC ELF32.  */
       rtx realsym = gen_rtx_SYMBOL_REF (Pmode, ggc_strdup (toc_label_name));
 
+      need_toc_init = 1;
       emit_insn (gen_elf_high (dest, realsym));
       emit_insn (gen_elf_low (dest, dest, realsym));
     }
@@ -27598,6 +27597,17 @@ rs6000_output_function_epilogue (FILE *file,
 
       fputs ("\t.align 2\n", file);
     }
+
+  /* Arrange to define .LCTOC1 label, if not already done.  */
+  if (need_toc_init)
+    {
+      need_toc_init = 0;
+      if (!toc_initialized)
+	{
+	  switch_to_section (toc_section);
+	  switch_to_section (current_function_section ());
+	}
+    }
 }
 
 /* -fsplit-stack support.  */
@@ -31745,6 +31755,7 @@ rs6000_elf_declare_function_name (FILE *file, const char *name, tree decl)
 
       fprintf (file, "\t.long ");
       assemble_name (file, toc_label_name);
+      need_toc_init = 1;
       putc ('-', file);
       ASM_GENERATE_INTERNAL_LABEL (buf, "LCF", rs6000_pic_labelno);
       assemble_name (file, buf);
@@ -32137,6 +32148,7 @@ rs6000_xcoff_file_start (void)
   fputc ('\n', asm_out_file);
   if (write_symbols != NO_DEBUG)
     switch_to_section (private_data_section);
+  switch_to_section (toc_section);
   switch_to_section (text_section);
   if (profile_flag)
     fprintf (asm_out_file, "\t.extern %s\n", RS6000_MCOUNT);
diff --git a/gcc/config/rs6000/rs6000.md b/gcc/config/rs6000/rs6000.md
index 6e22c52..fe19853 100644
--- a/gcc/config/rs6000/rs6000.md
+++ b/gcc/config/rs6000/rs6000.md
@@ -9475,6 +9475,8 @@
   "*
 {
   char buf[30];
+  extern int need_toc_init;
+  need_toc_init = 1;
   ASM_GENERATE_INTERNAL_LABEL (buf, \"LCTOC\", 1);
   operands[1] = gen_rtx_SYMBOL_REF (Pmode, ggc_strdup (buf));
   operands[2] = gen_rtx_REG (Pmode, 2);
@@ -9492,6 +9494,8 @@
   "*
 {
   char buf[30];
+  extern int need_toc_init;
+  need_toc_init = 1;
 #ifdef TARGET_RELOCATABLE
   ASM_GENERATE_INTERNAL_LABEL (buf, \"LCTOC\",
 			       !TARGET_MINIMAL_TOC || TARGET_RELOCATABLE);

-- 
Alan Modra
Australia Development Lab, IBM