rs6000: Add -msplit-patch-nops (PR112980)

as the bug report details some uses of -fpatchable-function-entry
aren't happy with the "before" NOPs being inserted between global and
local entry point on powerpc.  We want the before NOPs be in front
of the global entry point.  That means that the patching NOPs aren't
consecutive for dual entry point functions, but for these usecases
that's not the problem.  But let us support both under the control
of a new target option: -msplit-patch-nops.

	gcc/

	PR target/112980
	* config/rs6000/rs6000.opt (msplit-patch-nops): New option.
	* doc/invoke.texi (RS/6000 and PowerPC Options): Document it.
	* config/rs6000/rs6000.h (machine_function.stop_patch_area_print):
	New member.
	* config/rs6000/rs6000.cc (rs6000_print_patchable_function_entry):
	Emit split nops under control of that one.
	* config/rs6000/rs6000-logue.cc (rs6000_output_function_prologue):
	Add handling of split patch nops.

gcc/config/rs6000/rs6000-logue.cc

@@ -4005,8 +4005,8 @@ rs6000_output_function_prologue (FILE *file)
 
       unsigned short patch_area_size = crtl->patch_area_size;
       unsigned short patch_area_entry = crtl->patch_area_entry;
-      /* Need to emit the patching area.  */
-      if (patch_area_size > 0)
+      /* Emit non-split patching area now.  */
+      if (!TARGET_SPLIT_PATCH_NOPS && patch_area_size > 0)
 	{
 	  cfun->machine->global_entry_emitted = true;
 	  /* As ELFv2 ABI shows, the allowable bytes between the global
@@ -4027,7 +4027,6 @@ rs6000_output_function_prologue (FILE *file)
 		       patch_area_entry);
 	      rs6000_print_patchable_function_entry (file, patch_area_entry,
 						     true);
-	      patch_area_size -= patch_area_entry;
 	    }
 	}
 
@@ -4037,9 +4036,13 @@ rs6000_output_function_prologue (FILE *file)
       assemble_name (file, name);
       fputs ("\n", file);
       /* Emit the nops after local entry.  */
-      if (patch_area_size > 0)
-	rs6000_print_patchable_function_entry (file, patch_area_size,
-					       patch_area_entry == 0);
+      if (patch_area_size > patch_area_entry)
+	{
+	  patch_area_size -= patch_area_entry;
+	  cfun->machine->stop_patch_area_print = false;
+	  rs6000_print_patchable_function_entry (file, patch_area_size,
+						 patch_area_entry == 0);
+	}
     }
 
   else if (rs6000_pcrel_p ())

gcc/config/rs6000/rs6000.cc

@@ -15245,11 +15245,25 @@ rs6000_print_patchable_function_entry (FILE *file,
 {
   bool global_entry_needed_p = rs6000_global_entry_point_prologue_needed_p ();
   /* For a function which needs global entry point, we will emit the
-     patchable area before and after local entry point under the control of
-     cfun->machine->global_entry_emitted, see the handling in function
-     rs6000_output_function_prologue.  */
-  if (!global_entry_needed_p || cfun->machine->global_entry_emitted)
+     patchable area when it isn't split before and after local entry point
+     under the control of cfun->machine->global_entry_emitted, see the
+     handling in function rs6000_output_function_prologue.  */
+  if (!TARGET_SPLIT_PATCH_NOPS
+      && (!global_entry_needed_p || cfun->machine->global_entry_emitted))
     default_print_patchable_function_entry (file, patch_area_size, record_p);
+
+  /* For split patch nops we emit the before nops (from generic code)
+     in front of the global entry point and after the local entry point,
+     under the control of cfun->machine->stop_patch_area_print, see
+     rs6000_output_function_prologue and rs6000_elf_declare_function_name.  */
+  if (TARGET_SPLIT_PATCH_NOPS)
+    {
+      if (!cfun->machine->stop_patch_area_print)
+	default_print_patchable_function_entry (file, patch_area_size,
+						record_p);
+      else
+	gcc_assert (global_entry_needed_p);
+    }
 }
 
 enum rtx_code
@@ -21365,6 +21379,11 @@ rs6000_elf_declare_function_name (FILE *file, const char *name, tree decl)
       fprintf (file, "\t.previous\n");
     }
   ASM_OUTPUT_FUNCTION_LABEL (file, name, decl);
+  /* At this time, the "before" NOPs have been already emitted.
+     For split nops stop generic code from printing the "after" NOPs and
+     emit them just after local entry ourself later.  */
+  if (rs6000_global_entry_point_prologue_needed_p ())
+    cfun->machine->stop_patch_area_print = true;
 }
 
 static void rs6000_elf_file_end (void) ATTRIBUTE_UNUSED;

gcc/config/rs6000/rs6000.h

@@ -2422,6 +2422,12 @@ typedef struct GTY(()) machine_function
      local entry.  */
   bool global_entry_emitted;
   bool asm_redzone_clobber_seen;
+  /* With ELFv2 ABI dual entry points being adopted, generic framework
+     targetm.asm_out.print_patchable_function_entry would generate "after"
+     NOPs before local entry, which is wrong.  This flag is to stop it from
+     printing patch area before local entry, it is only useful when the
+     function requires dual entry points.  */
+  bool stop_patch_area_print;
 } machine_function;
 #endif
 

gcc/config/rs6000/rs6000.opt

@@ -300,6 +300,10 @@ mfull-toc
 Target
 Put everything in the regular TOC.
 
+msplit-patch-nops
+Target Var(TARGET_SPLIT_PATCH_NOPS) Init(0)
+Emit NOPs before global and after local entry point for -fpatchable-function-entry.
+
 mvrsave
 Target Var(TARGET_ALTIVEC_VRSAVE) Save
 Generate VRSAVE instructions when generating AltiVec code.

gcc/doc/invoke.texi

@@ -1320,6 +1320,7 @@ See RS/6000 and PowerPC Options.
 -mtraceback=@var{traceback_type}
 -maix-struct-return  -msvr4-struct-return
 -mabi=@var{abi-type}  -msecure-plt  -mbss-plt
+-msplit-patch-nops
 -mlongcall  -mno-longcall  -mpltseq  -mno-pltseq
 -mblock-move-inline-limit=@var{num}
 -mblock-compare-inline-limit=@var{num}
@@ -18805,11 +18806,12 @@ If @code{N=0}, no pad location is recorded.
 The NOP instructions are inserted at---and maybe before, depending on
 @var{M}---the function entry address, even before the prologue.  On
 PowerPC with the ELFv2 ABI, for a function with dual entry points,
-the local entry point is this function entry address.
+the local entry point is this function entry address by default.  See
+the @option{-msplit-patch-nops} option to change this.
 
 The maximum value of @var{N} and @var{M} is 65535.  On PowerPC with the
 ELFv2 ABI, for a function with dual entry points, the supported values
-for @var{M} are 0, 2, 6 and 14.
+for @var{M} are 0, 2, 6 and 14 when not using @option{-msplit-patch-nops}.
 @end table
 
 
@@ -31849,6 +31851,17 @@ requires @code{.plt} and @code{.got}
 sections that are both writable and executable.
 This is a PowerPC 32-bit SYSV ABI option.
 
+@opindex msplit-patch-nops
+@item -msplit-patch-nops
+When adding NOPs for a patchable area via the
+@option{-fpatchable-function-entry} option emit the ``before'' NOPs in front
+of the global entry point and the ``after'' NOPs after the local entry point.
+This makes the sequence of NOPs not consecutive when a global entry point
+is generated.  Without this option the NOPs are emitted directly before and
+after the local entry point, making them consecutive but moving global and
+local entry point further apart.  If only a single entry point is generated
+this option has no effect.
+
 @opindex misel
 @opindex mno-isel
 @item -misel