x86: Build only one __cpu_model/__cpu_features2 variables

GCC -O2 generated quite bad code for this function:

bool
f (void)
{
  return __builtin_cpu_supports("popcnt")
	 && __builtin_cpu_supports("ssse3");
}

f:
	movl	__cpu_model+12(%rip), %edx
	movl	%edx, %eax
	shrl	$6, %eax
	andl	$1, %eax
	andl	$4, %edx
	movl	$0, %edx
	cmove	%edx, %eax
	ret

The problem was caused by the fact that internally every invocation of
__builtin_cpu_supports built a new variable __cpu_model and a new type
__processor_model.  Because of this, GIMPLE level optimizers weren't able
to CSE the loads of __cpu_model and optimize bit-operations properly.

Improve GCC -O2 code generation by caching __cpu_model and__cpu_features2
variables as well as their types:

f:
        movl    __cpu_model+12(%rip), %eax
        andl    $68, %eax
        cmpl    $68, %eax
        sete    %al
        ret

2021-05-05  Ivan Sorokin <vanyacpp@gmail.com>
	    H.J. Lu <hjl.tools@gmail.com>

gcc/

	PR target/91400
	* config/i386/i386-builtins.c (ix86_cpu_model_type_node): New.
	(ix86_cpu_model_var): Likewise.
	(ix86_cpu_features2_type_node): Likewise.
	(ix86_cpu_features2_var): Likewise.
	(fold_builtin_cpu): Cache __cpu_model and __cpu_features2 with
	their types.

gcc/testsuite/

	PR target/91400
	* gcc.target/i386/pr91400-1.c: New test.
	* gcc.target/i386/pr91400-2.c: Likewise.

diff --git a/gcc/config/i386/i386-builtins.c b/gcc/config/i386/i386-builtins.c
index b66911082abe0e8184aa6e758dd73a4ea5457037..8036aedebac9309cd7ed52cc1302758c46301968 100644 (file)
--- a/gcc/config/i386/i386-builtins.c
+++ b/gcc/config/i386/i386-builtins.c
@@ -2103,6 +2103,11 @@ make_var_decl (tree type, const char *name)
   return new_decl;
 }
 
+static GTY(()) tree ix86_cpu_model_type_node;
+static GTY(()) tree ix86_cpu_model_var;
+static GTY(()) tree ix86_cpu_features2_type_node;
+static GTY(()) tree ix86_cpu_features2_var;
+
 /* FNDECL is a __builtin_cpu_is or a __builtin_cpu_supports call that is folded
    into an integer defined in libgcc/config/i386/cpuinfo.c */
 
@@ -2114,12 +2119,16 @@ fold_builtin_cpu (tree fndecl, tree *args)
     = (enum ix86_builtins) DECL_MD_FUNCTION_CODE (fndecl);
   tree param_string_cst = NULL;
 
-  tree __processor_model_type = build_processor_model_struct ();
-  tree __cpu_model_var = make_var_decl (__processor_model_type,
-                                       "__cpu_model");
-
-
-  varpool_node::add (__cpu_model_var);
+  if (ix86_cpu_model_var == nullptr)
+    {
+      /* Build a single __cpu_model variable for all references to
+        __cpu_model so that GIMPLE level optimizers can CSE the loads
+        of __cpu_model and optimize bit-operations properly.  */
+      ix86_cpu_model_type_node = build_processor_model_struct ();
+      ix86_cpu_model_var = make_var_decl (ix86_cpu_model_type_node,
+                                         "__cpu_model");
+      varpool_node::add (ix86_cpu_model_var);
+    }
 
   gcc_assert ((args != NULL) && (*args != NULL));
 
@@ -2160,7 +2169,7 @@ fold_builtin_cpu (tree fndecl, tree *args)
          return integer_zero_node;
        }
 
-      field = TYPE_FIELDS (__processor_model_type);
+      field = TYPE_FIELDS (ix86_cpu_model_type_node);
       field_val = processor_alias_table[i].model;
 
       /* CPU types are stored in the next field.  */
@@ -2179,7 +2188,7 @@ fold_builtin_cpu (tree fndecl, tree *args)
        }
 
       /* Get the appropriate field in __cpu_model.  */
-      ref = build3 (COMPONENT_REF, TREE_TYPE (field), __cpu_model_var,
+      ref = build3 (COMPONENT_REF, TREE_TYPE (field), ix86_cpu_model_var,
                    field, NULL_TREE);
 
       /* Check the value.  */
@@ -2212,13 +2221,22 @@ fold_builtin_cpu (tree fndecl, tree *args)
 
       if (isa_names_table[i].feature >= 32)
        {
-         tree index_type
-           = build_index_type (size_int (SIZE_OF_CPU_FEATURES));
-         tree type = build_array_type (unsigned_type_node, index_type);
-         tree __cpu_features2_var = make_var_decl (type,
-                                                   "__cpu_features2");
+         if (ix86_cpu_features2_var == nullptr)
+           {
+             /* Build a single __cpu_features2 variable for all
+                references to __cpu_features2 so that GIMPLE level
+                optimizers can CSE the loads of __cpu_features2 and
+                optimize bit-operations properly.  */
+             tree index_type
+               = build_index_type (size_int (SIZE_OF_CPU_FEATURES));
+             ix86_cpu_features2_type_node
+               = build_array_type (unsigned_type_node, index_type);
+             ix86_cpu_features2_var
+               = make_var_decl (ix86_cpu_features2_type_node,
+                                "__cpu_features2");
+             varpool_node::add (ix86_cpu_features2_var);
+           }
 
-         varpool_node::add (__cpu_features2_var);
          for (unsigned int j = 0; j < SIZE_OF_CPU_FEATURES; j++)
            if (isa_names_table[i].feature < (32 + 32 + j * 32))
              {
@@ -2226,7 +2244,7 @@ fold_builtin_cpu (tree fndecl, tree *args)
                                    - (32 + j * 32)));
                tree index = size_int (j);
                array_elt = build4 (ARRAY_REF, unsigned_type_node,
-                                   __cpu_features2_var,
+                                   ix86_cpu_features2_var,
                                    index, NULL_TREE, NULL_TREE);
                /* Return __cpu_features2[index] & field_val  */
                final = build2 (BIT_AND_EXPR, unsigned_type_node,
@@ -2237,13 +2255,13 @@ fold_builtin_cpu (tree fndecl, tree *args)
              }
        }
 
-      field = TYPE_FIELDS (__processor_model_type);
+      field = TYPE_FIELDS (ix86_cpu_model_type_node);
       /* Get the last field, which is __cpu_features.  */
       while (DECL_CHAIN (field))
         field = DECL_CHAIN (field);
 
       /* Get the appropriate field: __cpu_model.__cpu_features  */
-      ref = build3 (COMPONENT_REF, TREE_TYPE (field), __cpu_model_var,
+      ref = build3 (COMPONENT_REF, TREE_TYPE (field), ix86_cpu_model_var,
                    field, NULL_TREE);
 
       /* Access the 0th element of __cpu_features array.  */

diff --git a/gcc/testsuite/gcc.target/i386/pr91400-1.c b/gcc/testsuite/gcc.target/i386/pr91400-1.c
new file mode 100644 (file)
index 0000000..6124058
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr91400-1.c
@@ -0,0 +1,14 @@
+/* PR target/91400 */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+/* { dg-final { scan-assembler-times "andl" 1 } } */
+/* { dg-final { scan-assembler-times "cmpl" 1 } } */
+/* { dg-final { scan-assembler-times "sete" 1 } } */
+/* { dg-final { scan-assembler-not "cmove" } } */
+
+_Bool
+f (void)
+{
+  return __builtin_cpu_supports("popcnt")
+        && __builtin_cpu_supports("ssse3");
+}

diff --git a/gcc/testsuite/gcc.target/i386/pr91400-2.c b/gcc/testsuite/gcc.target/i386/pr91400-2.c
new file mode 100644 (file)
index 0000000..1af5a2f
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr91400-2.c
@@ -0,0 +1,14 @@
+/* PR target/91400 */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+/* { dg-final { scan-assembler-times "andl" 1 } } */
+/* { dg-final { scan-assembler-times "cmpl" 1 } } */
+/* { dg-final { scan-assembler-times "sete" 1 } } */
+/* { dg-final { scan-assembler-not "cmove" } } */
+
+_Bool
+f (void)
+{
+  return __builtin_cpu_supports("avx512vnni")
+        && __builtin_cpu_supports("3dnow");
+}