From cd1c07667495e7dd991cfcd0637eddf2bb65eac9 Mon Sep 17 00:00:00 2001
From: Michael Forney <mforney@mforney.org>
Date: Tue, 12 Mar 2019 18:43:14 -0700
Subject: Implement __builtin_constant_p

---
 decl.h                       |  1 +
 expr.c                       |  6 ++++++
 scope.c                      | 19 ++++++++++---------
 tests/builtin-constant-p.c   |  3 +++
 tests/builtin-constant-p.qbe |  2 ++
 5 files changed, 22 insertions(+), 9 deletions(-)
 create mode 100644 tests/builtin-constant-p.c
 create mode 100644 tests/builtin-constant-p.qbe

diff --git a/decl.h b/decl.h
index 4abbbac..98fd768 100644
--- a/decl.h
+++ b/decl.h
@@ -14,6 +14,7 @@ enum linkage {
 
 enum builtinkind {
 	BUILTINALLOCA,
+	BUILTINCONSTANTP,
 	BUILTININFF,
 	BUILTINNANF,
 	BUILTINOFFSETOF,
diff --git a/expr.c b/expr.c
index 4dd16a8..b6e7bbc 100644
--- a/expr.c
+++ b/expr.c
@@ -405,6 +405,8 @@ primaryexpr(struct scope *s)
 	return e;
 }
 
+static struct expression *condexpr(struct scope *);
+
 static struct expression *
 builtinfunc(struct scope *s, enum builtinkind kind)
 {
@@ -419,6 +421,10 @@ builtinfunc(struct scope *s, enum builtinkind kind)
 		e->builtin.kind = BUILTINALLOCA;
 		e->builtin.arg = exprconvert(assignexpr(s), &typeulong);
 		break;
+	case BUILTINCONSTANTP:
+		/* XXX: does this need to consider address constants? */
+		e = mkconstexpr(&typeint, eval(condexpr(s))->kind == EXPRCONST);
+		break;
 	case BUILTININFF:
 		e = mkexpr(EXPRCONST, &typefloat, 0);
 		/* TODO: use INFINITY here when we can handle musl's math.h */
diff --git a/scope.c b/scope.c
index 1bcd31f..c557f47 100644
--- a/scope.c
+++ b/scope.c
@@ -17,15 +17,16 @@ scopeinit(void)
 		char *name;
 		struct declaration decl;
 	} builtins[] = {
-		{"__builtin_alloca",   {.kind = DECLBUILTIN, .builtin = BUILTINALLOCA}},
-		{"__builtin_inff",     {.kind = DECLBUILTIN, .builtin = BUILTININFF}},
-		{"__builtin_nanf",     {.kind = DECLBUILTIN, .builtin = BUILTINNANF}},
-		{"__builtin_offsetof", {.kind = DECLBUILTIN, .builtin = BUILTINOFFSETOF}},
-		{"__builtin_va_arg",   {.kind = DECLBUILTIN, .builtin = BUILTINVAARG}},
-		{"__builtin_va_copy",  {.kind = DECLBUILTIN, .builtin = BUILTINVACOPY}},
-		{"__builtin_va_end",   {.kind = DECLBUILTIN, .builtin = BUILTINVAEND}},
-		{"__builtin_va_list",  {.kind = DECLTYPE, .type = &typevalist}},
-		{"__builtin_va_start", {.kind = DECLBUILTIN, .builtin = BUILTINVASTART}},
+		{"__builtin_alloca",     {.kind = DECLBUILTIN, .builtin = BUILTINALLOCA}},
+		{"__builtin_constant_p", {.kind = DECLBUILTIN, .builtin = BUILTINCONSTANTP}},
+		{"__builtin_inff",       {.kind = DECLBUILTIN, .builtin = BUILTININFF}},
+		{"__builtin_nanf",       {.kind = DECLBUILTIN, .builtin = BUILTINNANF}},
+		{"__builtin_offsetof",   {.kind = DECLBUILTIN, .builtin = BUILTINOFFSETOF}},
+		{"__builtin_va_arg",     {.kind = DECLBUILTIN, .builtin = BUILTINVAARG}},
+		{"__builtin_va_copy",    {.kind = DECLBUILTIN, .builtin = BUILTINVACOPY}},
+		{"__builtin_va_end",     {.kind = DECLBUILTIN, .builtin = BUILTINVAEND}},
+		{"__builtin_va_list",    {.kind = DECLTYPE, .type = &typevalist}},
+		{"__builtin_va_start",   {.kind = DECLBUILTIN, .builtin = BUILTINVASTART}},
 	};
 	struct builtin *b;
 
diff --git a/tests/builtin-constant-p.c b/tests/builtin-constant-p.c
new file mode 100644
index 0000000..fa16ed3
--- /dev/null
+++ b/tests/builtin-constant-p.c
@@ -0,0 +1,3 @@
+int f(void);
+int x = __builtin_constant_p(1+2*3);
+int y = __builtin_constant_p(f());
diff --git a/tests/builtin-constant-p.qbe b/tests/builtin-constant-p.qbe
new file mode 100644
index 0000000..f92388f
--- /dev/null
+++ b/tests/builtin-constant-p.qbe
@@ -0,0 +1,2 @@
+export data $x = align 4 { w 1, }
+export data $y = align 4 { w 0, }
-- 
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