From 2cbd75bbab472b6861dc0ae806e41cf139518fe6 Mon Sep 17 00:00:00 2001
From: Michael Forney <mforney@mforney.org>
Date: Fri, 22 Feb 2019 12:25:50 -0800
Subject: Implement __builtin_alloca

---
 decl.c                   |  1 +
 decl.h                   |  1 +
 expr.c                   | 10 +++++-----
 expr.h                   |  1 +
 main.c                   |  1 +
 qbe.c                    |  3 +++
 tests/builtin-alloca.c   |  3 +++
 tests/builtin-alloca.qbe | 12 ++++++++++++
 8 files changed, 27 insertions(+), 5 deletions(-)
 create mode 100644 tests/builtin-alloca.c
 create mode 100644 tests/builtin-alloca.qbe

diff --git a/decl.c b/decl.c
index 67fbef3..b789708 100644
--- a/decl.c
+++ b/decl.c
@@ -24,6 +24,7 @@ struct declaration builtinvaarg = {.kind = DECLBUILTIN};
 struct declaration builtinvacopy = {.kind = DECLBUILTIN};
 struct declaration builtinvaend = {.kind = DECLBUILTIN};
 struct declaration builtinoffsetof = {.kind = DECLBUILTIN};
+struct declaration builtinalloca = {.kind = DECLBUILTIN};
 
 static struct list tentativedefns = {&tentativedefns, &tentativedefns};
 
diff --git a/decl.h b/decl.h
index db3a956..0fb081b 100644
--- a/decl.h
+++ b/decl.h
@@ -31,6 +31,7 @@ extern struct declaration builtinvaarg;
 extern struct declaration builtinvacopy;
 extern struct declaration builtinvaend;
 extern struct declaration builtinoffsetof;
+extern struct declaration builtinalloca;
 
 struct declaration *mkdecl(enum declarationkind, struct type *, enum linkage);
 _Bool decl(struct scope *, struct function *);
diff --git a/expr.c b/expr.c
index a68f5d8..7de75f3 100644
--- a/expr.c
+++ b/expr.c
@@ -443,26 +443,22 @@ postfixexpr(struct scope *s, struct expression *r)
 					expect(TCOMMA, "after va_list");
 					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 == &builtinvacopy) {
 					e = mkexpr(EXPRASSIGN, typevalist.base, 0);
 					e->assign.l = mkunaryexpr(TMUL, exprconvert(assignexpr(s), &typevalistptr));
 					expect(TCOMMA, "after target va_list");
 					e->assign.r = mkunaryexpr(TMUL, exprconvert(assignexpr(s), &typevalistptr));
-					expect(TRPAREN, "after source va_list");
 					e = exprconvert(e, &typevoid);
 				} else if (r->ident.decl == &builtinvaend) {
 					e = mkexpr(EXPRBUILTIN, &typevoid, 0);
 					e->builtin.kind = BUILTINVAEND;
 					exprconvert(assignexpr(s), &typevalistptr);
-					expect(TRPAREN, "after va_list");
 				} else if (r->ident.decl == &builtinoffsetof) {
 					t = typename(s);
 					expect(TCOMMA, "after type name");
@@ -474,10 +470,14 @@ postfixexpr(struct scope *s, struct expression *r)
 						error(&tok.loc, "struct/union has no member named '%s'", name);
 					e = mkconstexpr(&typeulong, offset);
 					free(name);
-					expect(TRPAREN, "after member name");
+				} else if (r->ident.decl == &builtinalloca) {
+					e = mkexpr(EXPRBUILTIN, mkpointertype(&typevoid), 0);
+					e->builtin.kind = BUILTINALLOCA;
+					e->builtin.arg = exprconvert(assignexpr(s), &typeulong);
 				} else {
 					fatal("internal error; unknown builtin");
 				}
+				expect(TRPAREN, "after builtin parameters");
 				break;
 			}
 			lvalueconvert(r);
diff --git a/expr.h b/expr.h
index a6cac6d..f3ccd69 100644
--- a/expr.h
+++ b/expr.h
@@ -81,6 +81,7 @@ struct expression {
 				BUILTINVASTART,
 				BUILTINVAARG,
 				BUILTINVAEND,
+				BUILTINALLOCA,
 			} kind;
 			struct expression *arg;
 		} builtin;
diff --git a/main.c b/main.c
index db0132b..11f37b2 100644
--- a/main.c
+++ b/main.c
@@ -59,6 +59,7 @@ main(int argc, char *argv[])
 		scopeputdecl(&filescope, "__builtin_va_arg", &builtinvaarg);
 		scopeputdecl(&filescope, "__builtin_va_end", &builtinvaend);
 		scopeputdecl(&filescope, "__builtin_offsetof", &builtinoffsetof);
+		scopeputdecl(&filescope, "__builtin_alloca", &builtinalloca);
 		while (tok.kind != TEOF) {
 			if (!decl(&filescope, NULL))
 				error(&tok.loc, "expected declaration or function definition");
diff --git a/qbe.c b/qbe.c
index 7cc0719..4332b9c 100644
--- a/qbe.c
+++ b/qbe.c
@@ -830,6 +830,9 @@ funcexpr(struct function *f, struct expression *e)
 		case BUILTINVAEND:
 			/* no-op */
 			break;
+		case BUILTINALLOCA:
+			l = funcexpr(f, e->builtin.arg);
+			return funcinst(f, IALLOC16, &iptr, (struct value *[]){l});
 		default:
 			fatal("internal error: unimplemented builtin");
 		}
diff --git a/tests/builtin-alloca.c b/tests/builtin-alloca.c
new file mode 100644
index 0000000..f086f19
--- /dev/null
+++ b/tests/builtin-alloca.c
@@ -0,0 +1,3 @@
+void f(void) {
+	int *x = __builtin_alloca(32);
+}
diff --git a/tests/builtin-alloca.qbe b/tests/builtin-alloca.qbe
new file mode 100644
index 0000000..75a1fe1
--- /dev/null
+++ b/tests/builtin-alloca.qbe
@@ -0,0 +1,12 @@
+export
+function $f() {
+@start.1
+	%.1 =l alloc8 8
+@body.2
+	%.2 =l add %.1, 0
+	%.3 =l extsw 32
+	%.4 =l alloc16 %.3
+	%.5 =l copy %.4
+	storel %.5, %.2
+	ret
+}
-- 
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