From 3cc28c8428306a66350ef3722d45ed8c49bc6f15 Mon Sep 17 00:00:00 2001
From: Michael Forney <mforney@mforney.org>
Date: Wed, 3 Jul 2019 00:18:50 -0700
Subject: Implement no-op __builtin_expect

---
 cc.h                    | 1 +
 expr.c                  | 7 +++++++
 scope.c                 | 1 +
 test/builtin-expect.c   | 4 ++++
 test/builtin-expect.qbe | 8 ++++++++
 5 files changed, 21 insertions(+)
 create mode 100644 test/builtin-expect.c
 create mode 100644 test/builtin-expect.qbe

diff --git a/cc.h b/cc.h
index 0c0d08b..9b0989e 100644
--- a/cc.h
+++ b/cc.h
@@ -236,6 +236,7 @@ enum linkage {
 enum builtinkind {
 	BUILTINALLOCA,
 	BUILTINCONSTANTP,
+	BUILTINEXPECT,
 	BUILTININFF,
 	BUILTINNANF,
 	BUILTINOFFSETOF,
diff --git a/expr.c b/expr.c
index 591d80a..171c239 100644
--- a/expr.c
+++ b/expr.c
@@ -565,6 +565,13 @@ builtinfunc(struct scope *s, enum builtinkind kind)
 	case BUILTINCONSTANTP:
 		e = mkconstexpr(&typeint, eval(condexpr(s), EVALARITH)->kind == EXPRCONST);
 		break;
+	case BUILTINEXPECT:
+		/* just a no-op for now */
+		/* TODO: check that the expression and the expected value have type 'long' */
+		e = assignexpr(s);
+		expect(TCOMMA, "after expression");
+		delexpr(assignexpr(s));
+		break;
 	case BUILTININFF:
 		e = mkexpr(EXPRCONST, &typefloat);
 		/* TODO: use INFINITY here when we can handle musl's math.h */
diff --git a/scope.c b/scope.c
index 615d1fe..72025f5 100644
--- a/scope.c
+++ b/scope.c
@@ -16,6 +16,7 @@ scopeinit(void)
 	} builtins[] = {
 		{"__builtin_alloca",     {.kind = DECLBUILTIN, .builtin = BUILTINALLOCA}},
 		{"__builtin_constant_p", {.kind = DECLBUILTIN, .builtin = BUILTINCONSTANTP}},
+		{"__builtin_expect",     {.kind = DECLBUILTIN, .builtin = BUILTINEXPECT}},
 		{"__builtin_inff",       {.kind = DECLBUILTIN, .builtin = BUILTININFF}},
 		{"__builtin_nanf",       {.kind = DECLBUILTIN, .builtin = BUILTINNANF}},
 		{"__builtin_offsetof",   {.kind = DECLBUILTIN, .builtin = BUILTINOFFSETOF}},
diff --git a/test/builtin-expect.c b/test/builtin-expect.c
new file mode 100644
index 0000000..aac5ede
--- /dev/null
+++ b/test/builtin-expect.c
@@ -0,0 +1,4 @@
+int x;
+int main(void) {
+	return __builtin_expect(x, 0);
+}
diff --git a/test/builtin-expect.qbe b/test/builtin-expect.qbe
new file mode 100644
index 0000000..73e3b42
--- /dev/null
+++ b/test/builtin-expect.qbe
@@ -0,0 +1,8 @@
+export
+function w $main() {
+@start.1
+@body.2
+	%.1 =w loadsw $x
+	ret %.1
+}
+export data $x = align 4 { z 4 }
-- 
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