[PATCH] i386: Make most MD builtins nothrow, leaf [PR112962]

[Jakub Jelinek]

Hi!

The following patch makes most of x86 MD builtins nothrow,leaf
(like most middle-end builtins are).  For -fnon-call-exceptions it
doesn't nothrow, better might be to still add it if the builtins
don't read or write memory and can't raise floating point exceptions,
but we don't have such information readily available, so the patch
uses just !flag_non_call_exceptions for now.
Not sure if we shouldn't have some exceptions for the leaf attribute,
e.g. wonder about EMMS/FEMMS and the various xsave/xrstor etc. builtins,
pedantically none of those builtins do anything that leaf functions
are forbidden to do (having callbacks, calling functions from current TU,
longjump into the current TU), but sometimes non-leaf is also used on
really complex functions to prevent some unwanted optimizations.
That said, haven't run into any problems as is with the patch.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2023-12-13  Jakub Jelinek  <ja...@redhat.com>

        PR target/112962
        * config/i386/i386-builtins.cc (ix86_builtins): Increase by one
        element.
        (def_builtin): If not -fnon-call-exceptions, set TREE_NOTHROW on
        the builtin FUNCTION_DECL.  Add leaf attribute to DECL_ATTRIBUTES.
        (ix86_add_new_builtins): Likewise.

--- gcc/config/i386/i386-builtins.cc.jj 2023-10-13 19:34:43.767837029 +0200
+++ gcc/config/i386/i386-builtins.cc    2023-12-12 12:20:50.980071085 +0100
@@ -221,7 +221,7 @@ ix86_get_builtin_func_type (enum ix86_bu
 }
 
 /* Table for the ix86 builtin decls.  */
-static GTY(()) tree ix86_builtins[(int) IX86_BUILTIN_MAX];
+static GTY(()) tree ix86_builtins[(int) IX86_BUILTIN_MAX + 1];
 
 struct builtin_isa ix86_builtins_isa[(int) IX86_BUILTIN_MAX];
 
@@ -295,6 +295,12 @@ def_builtin (HOST_WIDE_INT mask, HOST_WI
                                       NULL, NULL_TREE);
          ix86_builtins[(int) code] = decl;
          ix86_builtins_isa[(int) code].set_and_not_built_p = false;
+         if (!flag_non_call_exceptions)
+           TREE_NOTHROW (decl) = 1;
+         if (ix86_builtins[(int) IX86_BUILTIN_MAX] == NULL_TREE)
+           ix86_builtins[(int) IX86_BUILTIN_MAX]
+             = build_tree_list (get_identifier ("leaf"), NULL_TREE);
+         DECL_ATTRIBUTES (decl) = ix86_builtins[(int) IX86_BUILTIN_MAX];
        }
       else
        {
@@ -393,6 +399,12 @@ ix86_add_new_builtins (HOST_WIDE_INT isa
            TREE_READONLY (decl) = 1;
          if (ix86_builtins_isa[i].pure_p)
            DECL_PURE_P (decl) = 1;
+         if (!flag_non_call_exceptions)
+           TREE_NOTHROW (decl) = 1;
+         if (ix86_builtins[(int) IX86_BUILTIN_MAX] == NULL_TREE)
+           ix86_builtins[(int) IX86_BUILTIN_MAX]
+             = build_tree_list (get_identifier ("leaf"), NULL_TREE);
+         DECL_ATTRIBUTES (decl) = ix86_builtins[(int) IX86_BUILTIN_MAX];
        }
     }
 

        Jakub