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Add ability to deduplicate types.

--- a/parse/parse.h

+++ b/parse/parse.h

@@ -142,6 +142,7 @@

 	char ispkglocal; /* Tyname: whether this is package local or not */

 	char isimport;   /* Tyname: whether tyis type was imported. */

 	char isreflect;  /* Tyname: whether this type has reflection info */

+	char isemitted;  /* Tyname: whether this type has been emitted */

 };

 struct Ucon {

@@ -420,6 +421,7 @@

 Type *mktype(Srcloc l, Ty ty);

 Type *tydup(Type *t); /* shallow duplicate; all subtypes/members/... kept */

+Type *tydedup(Type *t);

 Type *mktyvar(Srcloc l);

 Type *mktyparam(Srcloc l, char *name);

 Type *mktygeneric(Srcloc l, Node *name, Type **params, size_t nparams, Type *base);

--- a/parse/type.c

+++ b/parse/type.c

@@ -28,6 +28,7 @@

 Node **impltab;

 size_t nimpltab;

+static Htab *tydeduptab;

 /* Built in type constraints */

 static Trait *traits[Ntypes + 1][4];

 static int tybfmt(char *buf, size_t len, Type *t);

@@ -40,6 +41,20 @@

 int isstacktype(Type *t) { return stackness[tybase(t)->type]; }

+Type *tydedup(Type *ty)

+{

+	Type *had;

+

+	had = htget(tydeduptab, ty);

+	if (!had) {

+		htput(tydeduptab, ty, ty);

+		return ty;

+	}

+	/* if one is emitted, both are */

+	ty->isemitted = ty->isemitted || had->isemitted;

+	return had;

+}

+

 Type *mktype(Srcloc loc, Ty ty)

 {

 	Type *t;

@@ -644,11 +659,6 @@

 	t = (Type *)ty;

 	switch (t->type) {

-		/* Important: we want tyhash to be consistent cross-file, since it

-		 * is used in naming trait impls and such.

-		 *

-		 * We should find a better name.

-		 */

 	case Tyvar:	hash = inthash(t->tid);	break;

 	case Typaram:	hash = strhash(t->pname);	break;

 	case Tyunion:	hash = inthash(t->type);	break;

@@ -893,6 +903,7 @@

 	Type *ty;

 	Trait *tr;

+	tydeduptab = mkht(tyhash, tyeq);

 	/* this must be done after all the types are created, otherwise we will

 	 * clobber the memoized bunch of types with the type params. */

 #define Tc(c, n) \

@@ -948,6 +959,7 @@

 		ty = mktype(Zloc, t);	\

 		if (n) {	\

 			puttype(st, mkname(Zloc, n), ty);	\

+			htput(tydeduptab, ty, ty); \

 		}	\

 	}

 #include "types.def"