Short-cut generation of simple built-in functions

This patch short-circuits the builtins.c expansion code for a particular
gimple call if:

- the function has an associated internal function
- the target implements that internal function
- the call has no side effects

This allows a later patch to remove the builtins.c code, once calls with
side effects have been handled.

Tested on x86_64-linux-gnu, aarch64-linux-gnu and arm-linux-gnueabi.

gcc/
	* builtins.h (called_as_built_in): Declare.
	* builtins.c (called_as_built_in): Make external.
	* internal-fn.h (expand_internal_call): Define a variant that
	specifies the internal function explicitly.
	* internal-fn.c (expand_load_lanes_optab_fn)
	(expand_store_lanes_optab_fn, expand_ANNOTATE, expand_GOMP_SIMD_LANE)
	(expand_GOMP_SIMD_VF, expand_GOMP_SIMD_LAST_LANE)
	(expand_GOMP_SIMD_ORDERED_START, expand_GOMP_SIMD_ORDERED_END)
	(expand_UBSAN_NULL, expand_UBSAN_BOUNDS, expand_UBSAN_VPTR)
	(expand_UBSAN_OBJECT_SIZE, expand_ASAN_CHECK, expand_TSAN_FUNC_EXIT)
	(expand_UBSAN_CHECK_ADD, expand_UBSAN_CHECK_SUB)
	(expand_UBSAN_CHECK_MUL, expand_ADD_OVERFLOW, expand_SUB_OVERFLOW)
	(expand_MUL_OVERFLOW, expand_LOOP_VECTORIZED)
	(expand_mask_load_optab_fn, expand_mask_store_optab_fn)
	(expand_ABNORMAL_DISPATCHER, expand_BUILTIN_EXPECT, expand_VA_ARG)
	(expand_UNIQUE, expand_GOACC_DIM_SIZE, expand_GOACC_DIM_POS)
	(expand_GOACC_LOOP, expand_GOACC_REDUCTION, expand_direct_optab_fn)
	(expand_unary_optab_fn, expand_binary_optab_fn): Add an internal_fn
	argument.
	(internal_fn_expanders): Update prototype.
	(expand_internal_call): Define a variant that specifies the
	internal function explicitly. Use it to implement the previous
	interface.
	* cfgexpand.c (expand_call_stmt): Try to expand calls to built-in
	functions as calls to internal functions.

From-SVN: r230487

gcc/ChangeLog

 2015-11-17  Richard Sandiford  <richard.sandiford@arm.com>
 
+	* builtins.h (called_as_built_in): Declare.
+	* builtins.c (called_as_built_in): Make external.
+	* internal-fn.h (expand_internal_call): Define a variant that
+	specifies the internal function explicitly.
+	* internal-fn.c (expand_load_lanes_optab_fn)
+	(expand_store_lanes_optab_fn, expand_ANNOTATE, expand_GOMP_SIMD_LANE)
+	(expand_GOMP_SIMD_VF, expand_GOMP_SIMD_LAST_LANE)
+	(expand_GOMP_SIMD_ORDERED_START, expand_GOMP_SIMD_ORDERED_END)
+	(expand_UBSAN_NULL, expand_UBSAN_BOUNDS, expand_UBSAN_VPTR)
+	(expand_UBSAN_OBJECT_SIZE, expand_ASAN_CHECK, expand_TSAN_FUNC_EXIT)
+	(expand_UBSAN_CHECK_ADD, expand_UBSAN_CHECK_SUB)
+	(expand_UBSAN_CHECK_MUL, expand_ADD_OVERFLOW, expand_SUB_OVERFLOW)
+	(expand_MUL_OVERFLOW, expand_LOOP_VECTORIZED)
+	(expand_mask_load_optab_fn, expand_mask_store_optab_fn)
+	(expand_ABNORMAL_DISPATCHER, expand_BUILTIN_EXPECT, expand_VA_ARG)
+	(expand_UNIQUE, expand_GOACC_DIM_SIZE, expand_GOACC_DIM_POS)
+	(expand_GOACC_LOOP, expand_GOACC_REDUCTION, expand_direct_optab_fn)
+	(expand_unary_optab_fn, expand_binary_optab_fn): Add an internal_fn
+	argument.
+	(internal_fn_expanders): Update prototype.
+	(expand_internal_call): Define a variant that specifies the
+	internal function explicitly. Use it to implement the previous
+	interface.
+	* cfgexpand.c (expand_call_stmt): Try to expand calls to built-in
+	functions as calls to internal functions.
+
+2015-11-17  Richard Sandiford  <richard.sandiford@arm.com>
+
 	* Makefile.in (MOSTLYCLEANFILES): Add cfn-operators.pd.
 	(generated_files): Likewise.
 	(s-cfn-operators, cfn-operators.pd): New rules.

gcc/builtins.c

@@ -222,7 +222,7 @@ is_builtin_fn (tree decl)
    of the optimization level.  This means whenever a function is invoked with
    its "internal" name, which normally contains the prefix "__builtin".  */
 
-static bool
+bool
 called_as_built_in (tree node)
 {
   /* Note that we must use DECL_NAME, not DECL_ASSEMBLER_NAME_SET_P since

gcc/builtins.h

@@ -50,6 +50,7 @@ extern struct target_builtins *this_target_builtins;
 extern bool force_folding_builtin_constant_p;
 
 extern bool is_builtin_fn (tree);
+extern bool called_as_built_in (tree);
 extern bool get_object_alignment_1 (tree, unsigned int *,
 				    unsigned HOST_WIDE_INT *);
 extern unsigned int get_object_alignment (tree);

gcc/cfgexpand.c

@@ -2551,10 +2551,25 @@ expand_call_stmt (gcall *stmt)
       return;
     }
 
+  /* If this is a call to a built-in function and it has no effect other
+     than setting the lhs, try to implement it using an internal function
+     instead.  */
+  decl = gimple_call_fndecl (stmt);
+  if (gimple_call_lhs (stmt)
+      && !gimple_has_side_effects (stmt)
+      && (optimize || (decl && called_as_built_in (decl))))
+    {
+      internal_fn ifn = replacement_internal_fn (stmt);
+      if (ifn != IFN_LAST)
+	{
+	  expand_internal_call (ifn, stmt);
+	  return;
+	}
+    }
+
   exp = build_vl_exp (CALL_EXPR, gimple_call_num_args (stmt) + 3);
 
   CALL_EXPR_FN (exp) = gimple_call_fn (stmt);
-  decl = gimple_call_fndecl (stmt);
   builtin_p = decl && DECL_BUILT_IN (decl);
 
   /* If this is not a builtin function, the function type through which the

gcc/internal-fn.h

@@ -162,5 +162,6 @@ extern bool direct_internal_fn_supported_p (internal_fn, tree_pair);
 extern bool direct_internal_fn_supported_p (internal_fn, tree);
 
 extern void expand_internal_call (gcall *);
+extern void expand_internal_call (internal_fn, gcall *);
 
 #endif