Improve optimization of some builtins

Jan Hubicka hubicka@kam.mff.cuni.cz
Mon Nov 8 07:03:40 GMT 2021


Hi,
for nested functions we output call to builtin_dwarf_cfa which
initializes frame entry used only for debugging.  This however
prevents us from detecting functions containing nested functions
as const/pure or analyze side effects in modref.

builtin_dwarf_cfa is not documented and I wonder if it should be turned to
internal function. But I think we could consider functions using it const even
if in theory one can do things like test the return address and see the
difference between different frame addreses.

While doing so I also noticed that special_buitin_state handles quite few
builtins that are not special cased by ipa-modref.  They do not make
user visible loads/stores and thus I think they shoul dbe annotated by
".c" to make this explicit for both modref and PTA.

Finally I aded dwarf_cfa and similar return_address to list of simple
bulitins since it compiles to simple stack frame load and we consider
several other builtins doing so simple. 

lto-bootstrapped/regtested all languages on x86_64-linux, seems sane?

Honza

	* builtins.c (is_simple_builtin): Add builitin_dwarf_cfa
	and builtin_return_address.
	(builtin_fnspec): Annotate builtin_return,
	bulitin_eh_pointer, builtin_eh_filter, builtin_unwind_resume,
	builtin_cxa_end_cleanup, builtin_eh_copy_values,
	builtin_frame_address, builtin_apply_args,
	builtin_asan_before_dynamic_init, builtin_asan_after_dynamic_init,
	builtin_prefetch, builtin_dwarf_cfa, builtin_return_addrss
	as ".c"
	* ipa-pure-const.c (special_builtin_state): Add builtin_dwarf_cfa
	and builtin_return_address.
diff --git a/gcc/builtins.c b/gcc/builtins.c
index 7d0f61fc98b..43433e8d6ce 100644
--- a/gcc/builtins.c
+++ b/gcc/builtins.c
@@ -10711,6 +10711,8 @@ is_simple_builtin (tree decl)
       case BUILT_IN_VA_END:
       case BUILT_IN_STACK_SAVE:
       case BUILT_IN_STACK_RESTORE:
+      case BUILT_IN_DWARF_CFA:
+      case BUILT_IN_RETURN_ADDRESS:
 	/* Exception state returns or moves registers around.  */
       case BUILT_IN_EH_FILTER:
       case BUILT_IN_EH_POINTER:
@@ -11099,6 +11099,19 @@ builtin_fnspec (tree callee)
       CASE_BUILT_IN_TM_STORE (M256):
 	return ".cO ";
       case BUILT_IN_STACK_SAVE:
+      case BUILT_IN_RETURN:
+      case BUILT_IN_EH_POINTER:
+      case BUILT_IN_EH_FILTER:
+      case BUILT_IN_UNWIND_RESUME:
+      case BUILT_IN_CXA_END_CLEANUP:
+      case BUILT_IN_EH_COPY_VALUES:
+      case BUILT_IN_FRAME_ADDRESS:
+      case BUILT_IN_APPLY_ARGS:
+      case BUILT_IN_ASAN_BEFORE_DYNAMIC_INIT:
+      case BUILT_IN_ASAN_AFTER_DYNAMIC_INIT:
+      case BUILT_IN_PREFETCH:
+      case BUILT_IN_DWARF_CFA:
+      case BUILT_IN_RETURN_ADDRESS:
 	return ".c";
       case BUILT_IN_ASSUME_ALIGNED:
 	return "1cX ";
diff --git a/gcc/ipa-pure-const.c b/gcc/ipa-pure-const.c
index a84a4eb7ac0..e5048092939 100644
--- a/gcc/ipa-pure-const.c
+++ b/gcc/ipa-pure-const.c
@@ -529,6 +529,8 @@ special_builtin_state (enum pure_const_state_e *state, bool *looping,
       case BUILT_IN_APPLY_ARGS:
       case BUILT_IN_ASAN_BEFORE_DYNAMIC_INIT:
       case BUILT_IN_ASAN_AFTER_DYNAMIC_INIT:
+      case BUILT_IN_DWARF_CFA:
+      case BUILT_IN_RETURN_ADDRESS:
 	*looping = false;
 	*state = IPA_CONST;
 	return true;


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