be: Only accept the '=' and '+' asm constraint modifiers at the beginning and only one of them.

* GCC does this, too.
* This is sensible, because they apply to all alternatives of a multi-alternative constraint.
* This simplifies the implementation and makes some flags obsolete.

include/libfirm/be.h

@@ -40,19 +40,15 @@ typedef enum asm_constraint_flags_t {
 	ASM_CONSTRAINT_FLAG_NO_SUPPORT            = 1u << 3,
 	/** The input is also written to */
 	ASM_CONSTRAINT_FLAG_MODIFIER_WRITE        = 1u << 4,
-	/** the input is not written to */
-	ASM_CONSTRAINT_FLAG_MODIFIER_NO_WRITE     = 1u << 5,
 	/** the input is read */
-	ASM_CONSTRAINT_FLAG_MODIFIER_READ         = 1u << 6,
-	/** the input is not read */
-	ASM_CONSTRAINT_FLAG_MODIFIER_NO_READ      = 1u << 7,
+	ASM_CONSTRAINT_FLAG_MODIFIER_READ         = 1u << 5,
 	/** the value is modified before all inputs to the asm block
 	 * are handled. */
-	ASM_CONSTRAINT_FLAG_MODIFIER_EARLYCLOBBER = 1u << 8,
+	ASM_CONSTRAINT_FLAG_MODIFIER_EARLYCLOBBER = 1u << 6,
 	/** This operand and the following operand are commutative */
-	ASM_CONSTRAINT_FLAG_MODIFIER_COMMUTATIVE  = 1u << 9,
+	ASM_CONSTRAINT_FLAG_MODIFIER_COMMUTATIVE  = 1u << 7,
 	/** invalid constraint (due to parse error) */
-	ASM_CONSTRAINT_FLAG_INVALID               = 1u << 10
+	ASM_CONSTRAINT_FLAG_INVALID               = 1u << 8
 } asm_constraint_flags_t;
 ENUM_BITSET(asm_constraint_flags_t)
 

ir/be/bemain.c

@@ -153,17 +153,16 @@ asm_constraint_flags_t be_parse_asm_constraints(const char *constraint)
 {
 	initialize_isa();
 
-	asm_constraint_flags_t flags = ASM_CONSTRAINT_FLAG_NONE;
-	for (const char *c = constraint; *c != '\0'; ++c) {
+	asm_constraint_flags_t flags;
+	char            const *c = constraint;
+	switch (*c) {
+	case '=': ++c; flags = ASM_CONSTRAINT_FLAG_MODIFIER_WRITE; break;
+	case '+': ++c; flags = ASM_CONSTRAINT_FLAG_MODIFIER_READ | ASM_CONSTRAINT_FLAG_MODIFIER_WRITE; break;
+	default:       flags = ASM_CONSTRAINT_FLAG_MODIFIER_READ; break;
+	}
+
+	for (; *c != '\0'; ++c) {
 		switch (*c) {
-		case '=':
-			flags |= ASM_CONSTRAINT_FLAG_MODIFIER_WRITE;
-			flags |= ASM_CONSTRAINT_FLAG_MODIFIER_NO_READ;
-			break;
-		case '+':
-			flags |= ASM_CONSTRAINT_FLAG_MODIFIER_READ;
-			flags |= ASM_CONSTRAINT_FLAG_MODIFIER_WRITE;
-			break;
 		case '#':
 			/* text until comma is a comment */
 			while (*c != 0 && *c != ',')
@@ -176,23 +175,6 @@ asm_constraint_flags_t be_parse_asm_constraints(const char *constraint)
 		}
 	}
 
-	if ((
-	        flags & ASM_CONSTRAINT_FLAG_MODIFIER_WRITE &&
-	        flags & ASM_CONSTRAINT_FLAG_MODIFIER_NO_WRITE
-	    ) || (
-	        flags & ASM_CONSTRAINT_FLAG_MODIFIER_READ &&
-	        flags & ASM_CONSTRAINT_FLAG_MODIFIER_NO_READ
-	    )) {
-		flags |= ASM_CONSTRAINT_FLAG_INVALID;
-	}
-	if (!(flags & (ASM_CONSTRAINT_FLAG_MODIFIER_READ     |
-	               ASM_CONSTRAINT_FLAG_MODIFIER_WRITE    |
-	               ASM_CONSTRAINT_FLAG_MODIFIER_NO_WRITE |
-	               ASM_CONSTRAINT_FLAG_MODIFIER_NO_READ)
-	    )) {
-		flags |= ASM_CONSTRAINT_FLAG_MODIFIER_READ;
-	}
-
 	return flags;
 }