Re: [PATCH v2] implement constant-folding in __builtin_bswap*()

[Christopher Li <sparse@chrisli.org>]

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On Thu, Nov 24, 2016 at 9:36 AM, Luc Van Oostenryck
<luc.vanoostenryck@gmail.com> wrote:
> Small typo here: "Invaild"

Good catch. The corrected patch follows:

Chris

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--- sparse.chrisl.orig/symbol.h
+++ sparse.chrisl/symbol.h
@@ -130,6 +130,7 @@ struct symbol_op {
 
 extern int expand_safe_p(struct expression *expr, int cost);
 extern int expand_constant_p(struct expression *expr, int cost);
+extern int expand_bswap(struct expression *expr, int cost);
 
 #define SYM_ATTR_WEAK		0
 #define SYM_ATTR_NORMAL		1
--- sparse.chrisl.orig/lib.c
+++ sparse.chrisl/lib.c
@@ -819,40 +819,6 @@ void declare_builtin_functions(void)
 	add_pre_buffer("extern int __builtin_popcountl(unsigned long);\n");
 	add_pre_buffer("extern int __builtin_popcountll(unsigned long long);\n");
 
-	/* And byte swaps.. */
-	add_pre_buffer("extern unsigned short ____builtin_bswap16(unsigned short);\n");
-	add_pre_buffer("extern unsigned int ____builtin_bswap32(unsigned int);\n");
-	add_pre_buffer("extern unsigned long long ____builtin_bswap64(unsigned long long);\n");
-	add_pre_buffer("#define __sparse_constant_swab16(x) ((unsigned short)("
-		       "	(((unsigned short)(x) & (unsigned short)0x00ffU) << 8) |"
-		       "	(((unsigned short)(x) & (unsigned short)0xff00U) >> 8)))\n");
-	add_pre_buffer("#define __sparse_constant_swab32(x) ((unsigned int)("
-		       "	(((unsigned int)(x) & (unsigned int)0x000000ffUL) << 24) |"
-		       "	(((unsigned int)(x) & (unsigned int)0x0000ff00UL) <<  8) |"
-		       "	(((unsigned int)(x) & (unsigned int)0x00ff0000UL) >>  8) |"
-		       "	(((unsigned int)(x) & (unsigned int)0xff000000UL) >> 24)))\n");
-	add_pre_buffer("#define __sparse_constant_swab64(x) ((unsigned long long)("
-		       "	(((unsigned long long)(x) & (unsigned long long)0x00000000000000ffULL) << 56) |"
-		       "	(((unsigned long long)(x) & (unsigned long long)0x000000000000ff00ULL) << 40) |"
-		       "	(((unsigned long long)(x) & (unsigned long long)0x0000000000ff0000ULL) << 24) |"
-		       "	(((unsigned long long)(x) & (unsigned long long)0x00000000ff000000ULL) <<  8) |"
-		       "	(((unsigned long long)(x) & (unsigned long long)0x000000ff00000000ULL) >>  8) |"
-		       "	(((unsigned long long)(x) & (unsigned long long)0x0000ff0000000000ULL) >> 24) |"
-		       "	(((unsigned long long)(x) & (unsigned long long)0x00ff000000000000ULL) >> 40) |"
-		       "	(((unsigned long long)(x) & (unsigned long long)0xff00000000000000ULL) >> 56)))\n");
-	add_pre_buffer("#define __builtin_bswap16(x)"
-		       "	(__builtin_constant_p((unsigned short)(x)) ?"
-		       "	__sparse_constant_swab16(x) :"
-		       "	____builtin_bswap16(x))\n");
-	add_pre_buffer("#define __builtin_bswap32(x)"
-		       "	(__builtin_constant_p((unsigned int)(x)) ?"
-		       "	__sparse_constant_swab32(x) :"
-		       "	____builtin_bswap32(x))\n");
-	add_pre_buffer("#define __builtin_bswap64(x)"
-		       "	(__builtin_constant_p((unsigned long long)(x)) ?"
-		       "	__sparse_constant_swab64(x) :"
-		       "	____builtin_bswap64(x))\n");
-
 	/* And atomic memory access functions.. */
 	add_pre_buffer("extern int __sync_fetch_and_add(void *, ...);\n");
 	add_pre_buffer("extern int __sync_fetch_and_sub(void *, ...);\n");
--- sparse.chrisl.orig/ident-list.h
+++ sparse.chrisl/ident-list.h
@@ -35,6 +35,9 @@ IDENT_RESERVED(__sizeof_ptr__);
 IDENT_RESERVED(__builtin_types_compatible_p);
 IDENT_RESERVED(__builtin_offsetof);
 IDENT_RESERVED(__label__);
+IDENT(__builtin_bswap16);
+IDENT(__builtin_bswap32);
+IDENT(__builtin_bswap64);
 
 /* Attribute names */
 IDENT(packed); IDENT(__packed__);
--- sparse.chrisl.orig/symbol.c
+++ sparse.chrisl/symbol.c
@@ -773,6 +773,11 @@ static struct symbol_op choose_op = {
 	.args = arguments_choose,
 };
 
+static struct symbol_op bswap_op = {
+	.evaluate = evaluate_to_integer,
+	.expand = expand_bswap
+};
+
 /*
  * Builtin functions
  */
@@ -788,6 +793,9 @@ static struct sym_init {
 	{ "__builtin_warning", &builtin_fn_type, MOD_TOPLEVEL, &warning_op },
 	{ "__builtin_expect", &builtin_fn_type, MOD_TOPLEVEL, &expect_op },
 	{ "__builtin_choose_expr", &builtin_fn_type, MOD_TOPLEVEL, &choose_op },
+	{ "__builtin_bswap16", &builtin_fn_type, MOD_TOPLEVEL, &bswap_op },
+	{ "__builtin_bswap32", &builtin_fn_type, MOD_TOPLEVEL, &bswap_op },
+	{ "__builtin_bswap64", &builtin_fn_type, MOD_TOPLEVEL, &bswap_op },
 	{ NULL,		NULL,		0 }
 };
 
--- sparse.chrisl.orig/lib.h
+++ sparse.chrisl/lib.h
@@ -200,6 +200,11 @@ static inline struct instruction *first_
 	return first_ptr_list((struct ptr_list *)head);
 }
 
+static inline struct expression *first_expression(struct expression_list *head)
+{
+	return first_ptr_list((struct ptr_list *)head);
+}
+
 static inline pseudo_t first_pseudo(struct pseudo_list *head)
 {
 	return first_ptr_list((struct ptr_list *)head);
--- sparse.chrisl.orig/expand.c
+++ sparse.chrisl/expand.c
@@ -802,6 +802,46 @@ int expand_safe_p(struct expression *exp
 	return 0;
 }
 
+/* The arguments are constant if the cost of all of them is zero */
+int expand_bswap(struct expression *expr, int cost)
+{
+	struct symbol *sym;
+	struct expression_list *args = expr->args;
+	long long input;
+	int count;
+
+	if (cost)
+		return cost;
+
+	sym = expr->fn->ctype;
+	count = expression_list_size(args);
+	if (count != 1) {
+		sparse_error(expr->pos, "Invalid number of arguments for function %s (expected 1 got %d)",
+				show_ident(sym->ident), count);
+		return SIDE_EFFECTS;
+	}
+
+	input = const_expression_value(first_expression(args));
+
+	if (sym->ident == &__builtin_bswap16_ident) {
+		expr->value = __builtin_bswap16(input);
+		expr->ctype = &ushort_ctype;
+	} else if (sym->ident == &__builtin_bswap32_ident) {
+		expr->value = __builtin_bswap32(input);
+		expr->ctype = &uint_ctype;
+	} else if (sym->ident == &__builtin_bswap64_ident) {
+		expr->value = __builtin_bswap64(input);
+		expr->ctype = &ullong_ctype;
+	} else {
+		die("Unexpected __builtin_bswap symbol %s\n", show_ident(sym->ident));
+	}
+
+	expr->type = EXPR_VALUE;
+	expr->taint = 0;
+	return 0;
+}
+
+
 /*
  * expand a call expression with a symbol. This
  * should expand builtins.