From a0c394bdd0f0c554f504ee8119e8304551653562 Mon Sep 17 00:00:00 2001
From: Michael Forney <mforney@mforney.org>
Date: Wed, 13 Feb 2019 15:28:40 -0800
Subject: Implement __builtin_va_arg

---
 decl.c            |  1 +
 decl.h            |  2 +-
 expr.c            |  7 +++++++
 expr.h            |  1 +
 main.c            |  1 +
 qbe.c             |  3 +++
 tests/varargs.c   | 12 ++++++++++++
 tests/varargs.qbe | 22 ++++++++++++++++++++++
 8 files changed, 48 insertions(+), 1 deletion(-)
 create mode 100644 tests/varargs.c
 create mode 100644 tests/varargs.qbe

diff --git a/decl.c b/decl.c
index 235c975..4c89753 100644
--- a/decl.c
+++ b/decl.c
@@ -19,6 +19,7 @@
 #include "type.h"
 
 struct declaration builtinvastart = {.kind = DECLBUILTIN};
+struct declaration builtinvaarg = {.kind = DECLBUILTIN};
 struct declaration builtinvaend = {.kind = DECLBUILTIN};
 struct declaration builtinoffsetof = {.kind = DECLBUILTIN};
 
diff --git a/decl.h b/decl.h
index 4b3ef20..3e3c5af 100644
--- a/decl.h
+++ b/decl.h
@@ -25,7 +25,7 @@ struct declaration {
 struct scope;
 struct function;
 
-extern struct declaration builtinvastart, builtinvaend, builtinoffsetof;
+extern struct declaration builtinvastart, builtinvaarg, builtinvaend, builtinoffsetof;
 
 struct declaration *mkdecl(enum declarationkind, struct type *, enum linkage);
 _Bool decl(struct scope *, struct function *);
diff --git a/expr.c b/expr.c
index 70d8dbf..5973f67 100644
--- a/expr.c
+++ b/expr.c
@@ -410,6 +410,13 @@ postfixexpr(struct scope *s, struct expression *r)
 					free(expect(TIDENT, "after ','"));
 					// XXX: check that this was actually a parameter name?
 					expect(TRPAREN, "after parameter identifier");
+				} else if (r->ident.decl == &builtinvaarg) {
+					e = mkexpr(EXPRBUILTIN, NULL, 0);
+					e->builtin.kind = BUILTINVAARG;
+					e->builtin.arg = exprconvert(assignexpr(s), &typevalistptr);
+					expect(TCOMMA, "after va_list");
+					e->type = typename(s);
+					expect(TRPAREN, "after typename");
 				} else if (r->ident.decl == &builtinvaend) {
 					e = mkexpr(EXPRBUILTIN, &typevoid, 0);
 					e->builtin.kind = BUILTINVAEND;
diff --git a/expr.h b/expr.h
index 8269d22..5c8ef96 100644
--- a/expr.h
+++ b/expr.h
@@ -79,6 +79,7 @@ struct expression {
 		struct {
 			enum {
 				BUILTINVASTART,
+				BUILTINVAARG,
 				BUILTINVAEND,
 			} kind;
 			struct expression *arg;
diff --git a/main.c b/main.c
index fa50078..c8491eb 100644
--- a/main.c
+++ b/main.c
@@ -54,6 +54,7 @@ main(int argc, char *argv[])
 		}
 	} else {
 		scopeputdecl(&filescope, "__builtin_va_start", &builtinvastart);
+		scopeputdecl(&filescope, "__builtin_va_arg", &builtinvaarg);
 		scopeputdecl(&filescope, "__builtin_va_end", &builtinvaend);
 		scopeputdecl(&filescope, "__builtin_offsetof", &builtinoffsetof);
 		while (tok.kind != TEOF) {
diff --git a/qbe.c b/qbe.c
index fad1858..fde25e2 100644
--- a/qbe.c
+++ b/qbe.c
@@ -777,6 +777,9 @@ funcexpr(struct function *f, struct expression *e)
 			l = funcexpr(f, e->builtin.arg);
 			funcinst(f, IVASTART, NULL, (struct value *[]){l});
 			break;
+		case BUILTINVAARG:
+			l = funcexpr(f, e->builtin.arg);
+			return funcinst(f, IVAARG, e->type->repr, (struct value *[]){l});
 		case BUILTINVAEND:
 			/* no-op */
 			break;
diff --git a/tests/varargs.c b/tests/varargs.c
new file mode 100644
index 0000000..0b5a73d
--- /dev/null
+++ b/tests/varargs.c
@@ -0,0 +1,12 @@
+void f(int n, ...) {
+	__builtin_va_list ap;
+
+	__builtin_va_start(ap, n);
+	while (n) {
+		__builtin_va_arg(ap, int);
+		__builtin_va_arg(ap, float);
+		__builtin_va_arg(ap, char *);
+		--n;
+	}
+	__builtin_va_end(ap);
+}
diff --git a/tests/varargs.qbe b/tests/varargs.qbe
new file mode 100644
index 0000000..16db877
--- /dev/null
+++ b/tests/varargs.qbe
@@ -0,0 +1,22 @@
+export
+function $f(w %.1, ...) {
+@start.1
+	%.2 =l alloc4 4
+	storew %.1, %.2
+	%.3 =l alloc8 24
+@body.2
+	vastart %.3
+@while_cond.3
+	%.4 =w loadsw %.2
+	jnz %.4, @while_body.4, @while_join.5
+@while_body.4
+	%.5 =w vaarg %.3
+	%.6 =s vaarg %.3
+	%.7 =l vaarg %.3
+	%.8 =w loadsw %.2
+	%.9 =w sub %.8, 1
+	storew %.9, %.2
+	jmp @while_cond.3
+@while_join.5
+	ret
+}
-- 
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