Short-cut generation of simple built-in functions

[Richard Sandiford <richard dot sandiford at arm dot com>]

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.
OK to install?

Thanks,
Richard


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.

diff --git a/gcc/builtins.c b/gcc/builtins.c
index f65011e..bbcc7dc3 100644
--- a/gcc/builtins.c
+++ b/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
diff --git a/gcc/builtins.h b/gcc/builtins.h
index 917eb90..1d00068 100644
--- a/gcc/builtins.h
+++ b/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);
diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
index bfbc958..dc7d4f5 100644
--- a/gcc/cfgexpand.c
+++ b/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_vdef (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
diff --git a/gcc/internal-fn.c b/gcc/internal-fn.c
index 9f9f9cf..c03c0fc 100644
--- a/gcc/internal-fn.c
+++ b/gcc/internal-fn.c
@@ -103,7 +103,7 @@ get_multi_vector_move (tree array_type, convert_optab optab)
 /* Expand LOAD_LANES call STMT using optab OPTAB.  */
 
 static void
-expand_load_lanes_optab_fn (gcall *stmt, convert_optab optab)
+expand_load_lanes_optab_fn (internal_fn, gcall *stmt, convert_optab optab)
 {
   struct expand_operand ops[2];
   tree type, lhs, rhs;
@@ -127,7 +127,7 @@ expand_load_lanes_optab_fn (gcall *stmt, convert_optab optab)
 /* Expand STORE_LANES call STMT using optab OPTAB.  */
 
 static void
-expand_store_lanes_optab_fn (gcall *stmt, convert_optab optab)
+expand_store_lanes_optab_fn (internal_fn, gcall *stmt, convert_optab optab)
 {
   struct expand_operand ops[2];
   tree type, lhs, rhs;
@@ -149,7 +149,7 @@ expand_store_lanes_optab_fn (gcall *stmt, convert_optab optab)
 }
 
 static void
-expand_ANNOTATE (gcall *)
+expand_ANNOTATE (internal_fn, gcall *)
 {
   gcc_unreachable ();
 }
@@ -157,7 +157,7 @@ expand_ANNOTATE (gcall *)
 /* This should get expanded in adjust_simduid_builtins.  */
 
 static void
-expand_GOMP_SIMD_LANE (gcall *)
+expand_GOMP_SIMD_LANE (internal_fn, gcall *)
 {
   gcc_unreachable ();
 }
@@ -165,7 +165,7 @@ expand_GOMP_SIMD_LANE (gcall *)
 /* This should get expanded in adjust_simduid_builtins.  */
 
 static void
-expand_GOMP_SIMD_VF (gcall *)
+expand_GOMP_SIMD_VF (internal_fn, gcall *)
 {
   gcc_unreachable ();
 }
@@ -173,7 +173,7 @@ expand_GOMP_SIMD_VF (gcall *)
 /* This should get expanded in adjust_simduid_builtins.  */
 
 static void
-expand_GOMP_SIMD_LAST_LANE (gcall *)
+expand_GOMP_SIMD_LAST_LANE (internal_fn, gcall *)
 {
   gcc_unreachable ();
 }
@@ -181,7 +181,7 @@ expand_GOMP_SIMD_LAST_LANE (gcall *)
 /* This should get expanded in adjust_simduid_builtins.  */
 
 static void
-expand_GOMP_SIMD_ORDERED_START (gcall *)
+expand_GOMP_SIMD_ORDERED_START (internal_fn, gcall *)
 {
   gcc_unreachable ();
 }
@@ -189,7 +189,7 @@ expand_GOMP_SIMD_ORDERED_START (gcall *)
 /* This should get expanded in adjust_simduid_builtins.  */
 
 static void
-expand_GOMP_SIMD_ORDERED_END (gcall *)
+expand_GOMP_SIMD_ORDERED_END (internal_fn, gcall *)
 {
   gcc_unreachable ();
 }
@@ -197,7 +197,7 @@ expand_GOMP_SIMD_ORDERED_END (gcall *)
 /* This should get expanded in the sanopt pass.  */
 
 static void
-expand_UBSAN_NULL (gcall *)
+expand_UBSAN_NULL (internal_fn, gcall *)
 {
   gcc_unreachable ();
 }
@@ -205,7 +205,7 @@ expand_UBSAN_NULL (gcall *)
 /* This should get expanded in the sanopt pass.  */
 
 static void
-expand_UBSAN_BOUNDS (gcall *)
+expand_UBSAN_BOUNDS (internal_fn, gcall *)
 {
   gcc_unreachable ();
 }
@@ -213,7 +213,7 @@ expand_UBSAN_BOUNDS (gcall *)
 /* This should get expanded in the sanopt pass.  */
 
 static void
-expand_UBSAN_VPTR (gcall *)
+expand_UBSAN_VPTR (internal_fn, gcall *)
 {
   gcc_unreachable ();
 }
@@ -221,7 +221,7 @@ expand_UBSAN_VPTR (gcall *)
 /* This should get expanded in the sanopt pass.  */
 
 static void
-expand_UBSAN_OBJECT_SIZE (gcall *)
+expand_UBSAN_OBJECT_SIZE (internal_fn, gcall *)
 {
   gcc_unreachable ();
 }
@@ -229,7 +229,7 @@ expand_UBSAN_OBJECT_SIZE (gcall *)
 /* This should get expanded in the sanopt pass.  */
 
 static void
-expand_ASAN_CHECK (gcall *)
+expand_ASAN_CHECK (internal_fn, gcall *)
 {
   gcc_unreachable ();
 }
@@ -237,7 +237,7 @@ expand_ASAN_CHECK (gcall *)
 /* This should get expanded in the tsan pass.  */
 
 static void
-expand_TSAN_FUNC_EXIT (gcall *)
+expand_TSAN_FUNC_EXIT (internal_fn, gcall *)
 {
   gcc_unreachable ();
 }
@@ -1639,7 +1639,7 @@ expand_mul_overflow (location_t loc, tree lhs, tree arg0, tree arg1,
 /* Expand UBSAN_CHECK_ADD call STMT.  */
 
 static void
-expand_UBSAN_CHECK_ADD (gcall *stmt)
+expand_UBSAN_CHECK_ADD (internal_fn, gcall *stmt)
 {
   location_t loc = gimple_location (stmt);
   tree lhs = gimple_call_lhs (stmt);
@@ -1652,7 +1652,7 @@ expand_UBSAN_CHECK_ADD (gcall *stmt)
 /* Expand UBSAN_CHECK_SUB call STMT.  */
 
 static void
-expand_UBSAN_CHECK_SUB (gcall *stmt)
+expand_UBSAN_CHECK_SUB (internal_fn, gcall *stmt)
 {
   location_t loc = gimple_location (stmt);
   tree lhs = gimple_call_lhs (stmt);
@@ -1668,7 +1668,7 @@ expand_UBSAN_CHECK_SUB (gcall *stmt)
 /* Expand UBSAN_CHECK_MUL call STMT.  */
 
 static void
-expand_UBSAN_CHECK_MUL (gcall *stmt)
+expand_UBSAN_CHECK_MUL (internal_fn, gcall *stmt)
 {
   location_t loc = gimple_location (stmt);
   tree lhs = gimple_call_lhs (stmt);
@@ -1853,7 +1853,7 @@ expand_arith_overflow (enum tree_code code, gimple *stmt)
 /* Expand ADD_OVERFLOW STMT.  */
 
 static void
-expand_ADD_OVERFLOW (gcall *stmt)
+expand_ADD_OVERFLOW (internal_fn, gcall *stmt)
 {
   expand_arith_overflow (PLUS_EXPR, stmt);
 }
@@ -1861,7 +1861,7 @@ expand_ADD_OVERFLOW (gcall *stmt)
 /* Expand SUB_OVERFLOW STMT.  */
 
 static void
-expand_SUB_OVERFLOW (gcall *stmt)
+expand_SUB_OVERFLOW (internal_fn, gcall *stmt)
 {
   expand_arith_overflow (MINUS_EXPR, stmt);
 }
@@ -1869,7 +1869,7 @@ expand_SUB_OVERFLOW (gcall *stmt)
 /* Expand MUL_OVERFLOW STMT.  */
 
 static void
-expand_MUL_OVERFLOW (gcall *stmt)
+expand_MUL_OVERFLOW (internal_fn, gcall *stmt)
 {
   expand_arith_overflow (MULT_EXPR, stmt);
 }
@@ -1877,7 +1877,7 @@ expand_MUL_OVERFLOW (gcall *stmt)
 /* This should get folded in tree-vectorizer.c.  */
 
 static void
-expand_LOOP_VECTORIZED (gcall *)
+expand_LOOP_VECTORIZED (internal_fn, gcall *)
 {
   gcc_unreachable ();
 }
@@ -1885,7 +1885,7 @@ expand_LOOP_VECTORIZED (gcall *)
 /* Expand MASK_LOAD call STMT using optab OPTAB.  */
 
 static void
-expand_mask_load_optab_fn (gcall *stmt, direct_optab optab)
+expand_mask_load_optab_fn (internal_fn, gcall *stmt, direct_optab optab)
 {
   struct expand_operand ops[3];
   tree type, lhs, rhs, maskt;
@@ -1912,7 +1912,7 @@ expand_mask_load_optab_fn (gcall *stmt, direct_optab optab)
 /* Expand MASK_STORE call STMT using optab OPTAB.  */
 
 static void
-expand_mask_store_optab_fn (gcall *stmt, direct_optab optab)
+expand_mask_store_optab_fn (internal_fn, gcall *stmt, direct_optab optab)
 {
   struct expand_operand ops[3];
   tree type, lhs, rhs, maskt;
@@ -1935,12 +1935,12 @@ expand_mask_store_optab_fn (gcall *stmt, direct_optab optab)
 }
 
 static void
-expand_ABNORMAL_DISPATCHER (gcall *)
+expand_ABNORMAL_DISPATCHER (internal_fn, gcall *)
 {
 }
 
 static void
-expand_BUILTIN_EXPECT (gcall *stmt)
+expand_BUILTIN_EXPECT (internal_fn, gcall *stmt)
 {
   /* When guessing was done, the hints should be already stripped away.  */
   gcc_assert (!flag_guess_branch_prob || optimize == 0 || seen_error ());
@@ -1960,7 +1960,7 @@ expand_BUILTIN_EXPECT (gcall *stmt)
    should never be called.  */
 
 static void
-expand_VA_ARG (gcall *stmt ATTRIBUTE_UNUSED)
+expand_VA_ARG (internal_fn, gcall *)
 {
   gcc_unreachable ();
 }
@@ -1968,7 +1968,7 @@ expand_VA_ARG (gcall *stmt ATTRIBUTE_UNUSED)
 /* Expand the IFN_UNIQUE function according to its first argument.  */
 
 static void
-expand_UNIQUE (gcall *stmt)
+expand_UNIQUE (internal_fn, gcall *stmt)
 {
   rtx pattern = NULL_RTX;
   enum ifn_unique_kind kind
@@ -2014,7 +2014,7 @@ expand_UNIQUE (gcall *stmt)
 /* The size of an OpenACC compute dimension.  */
 
 static void
-expand_GOACC_DIM_SIZE (gcall *stmt)
+expand_GOACC_DIM_SIZE (internal_fn, gcall *stmt)
 {
   tree lhs = gimple_call_lhs (stmt);
 
@@ -2035,7 +2035,7 @@ expand_GOACC_DIM_SIZE (gcall *stmt)
 /* The position of an OpenACC execution engine along one compute axis.  */
 
 static void
-expand_GOACC_DIM_POS (gcall *stmt)
+expand_GOACC_DIM_POS (internal_fn, gcall *stmt)
 {
   tree lhs = gimple_call_lhs (stmt);
 
@@ -2056,7 +2056,7 @@ expand_GOACC_DIM_POS (gcall *stmt)
 /* This is expanded by oacc_device_lower pass.  */
 
 static void
-expand_GOACC_LOOP (gcall *stmt ATTRIBUTE_UNUSED)
+expand_GOACC_LOOP (internal_fn, gcall *)
 {
   gcc_unreachable ();
 }
@@ -2064,20 +2064,20 @@ expand_GOACC_LOOP (gcall *stmt ATTRIBUTE_UNUSED)
 /* This is expanded by oacc_device_lower pass.  */
 
 static void
-expand_GOACC_REDUCTION (gcall *stmt ATTRIBUTE_UNUSED)
+expand_GOACC_REDUCTION (internal_fn, gcall *)
 {
   gcc_unreachable ();
 }
 
-/* Expand call STMT using OPTAB, which has a single output operand and
-   NARGS input operands.  */
+/* Expand a call to FN using the operands in STMT.  FN has a single
+   output operand and NARGS input operands.  */
 
 static void
-expand_direct_optab_fn (gcall *stmt, direct_optab optab, unsigned int nargs)
+expand_direct_optab_fn (internal_fn fn, gcall *stmt, direct_optab optab,
+			unsigned int nargs)
 {
   expand_operand *ops = XALLOCAVEC (expand_operand, nargs + 1);
 
-  internal_fn fn = gimple_call_internal_fn (stmt);
   tree_pair types = direct_internal_fn_types (fn, stmt);
   insn_code icode = direct_optab_handler (optab, TYPE_MODE (types.first));
 
@@ -2115,11 +2115,11 @@ expand_direct_optab_fn (gcall *stmt, direct_optab optab, unsigned int nargs)
 
 /* Expanders for optabs that can use expand_direct_optab_fn.  */
 
-#define expand_unary_optab_fn(STMT, OPTAB) \
-  expand_direct_optab_fn (STMT, OPTAB, 1)
+#define expand_unary_optab_fn(FN, STMT, OPTAB) \
+  expand_direct_optab_fn (FN, STMT, OPTAB, 1)
 
-#define expand_binary_optab_fn(STMT, OPTAB) \
-  expand_direct_optab_fn (STMT, OPTAB, 2)
+#define expand_binary_optab_fn(FN, STMT, OPTAB) \
+  expand_direct_optab_fn (FN, STMT, OPTAB, 2)
 
 /* RETURN_TYPE and ARGS are a return type and argument list that are
    in principle compatible with FN (which satisfies direct_internal_fn_p).
@@ -2215,9 +2215,9 @@ direct_internal_fn_supported_p (internal_fn fn, tree type)
 
 #define DEF_INTERNAL_OPTAB_FN(CODE, FLAGS, OPTAB, TYPE) \
   static void						\
-  expand_##CODE (gcall *stmt)				\
+  expand_##CODE (internal_fn fn, gcall *stmt)		\
   {							\
-    expand_##TYPE##_optab_fn (stmt, OPTAB##_optab);	\
+    expand_##TYPE##_optab_fn (fn, stmt, OPTAB##_optab);	\
   }
 #include "internal-fn.def"
 
@@ -2227,16 +2227,24 @@ direct_internal_fn_supported_p (internal_fn fn, tree type)
        expand_<NAME> (gcall *stmt)
 
    where STMT is the statement that performs the call. */
-static void (*const internal_fn_expanders[]) (gcall *) = {
+static void (*const internal_fn_expanders[]) (internal_fn, gcall *) = {
 #define DEF_INTERNAL_FN(CODE, FLAGS, FNSPEC) expand_##CODE,
 #include "internal-fn.def"
   0
 };
 
+/* Expand STMT as though it were a call to internal function FN.  */
+
+void
+expand_internal_call (internal_fn fn, gcall *stmt)
+{
+  internal_fn_expanders[fn] (fn, stmt);
+}
+
 /* Expand STMT, which is a call to internal function FN.  */
 
 void
 expand_internal_call (gcall *stmt)
 {
-  internal_fn_expanders[(int) gimple_call_internal_fn (stmt)] (stmt);
+  expand_internal_call (gimple_call_internal_fn (stmt), stmt);
 }
diff --git a/gcc/internal-fn.h b/gcc/internal-fn.h
index 31e895e..5ee43b8 100644
--- a/gcc/internal-fn.h
+++ b/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