Compile time fmod evaluates to 0 #1195

releasenotes.md

@@ -17,6 +17,7 @@
 - Duplicate emit of expressions on negation would incorrectly compile negated macros.
 - Casting a slice address to its pointer type should not compile #1193.
 - Union is not properly zero-initialized with designated initializer #1194.
+- Compile time fmod evaluates to 0 #1195.
 
 ### Stdlib changes
 - Add 'zstr' variants for `string::new_format` / `string::tformat`.

src/compiler/compiler_internal.h

@@ -2015,6 +2015,7 @@ Float float_sub(Float op1, Float op2);
 Float float_mul(Float op1, Float op2);
 Float float_div(Float op1, Float op2);
 Float float_neg(Float op);
+Float float_rem(Float op1, Float op2);
 Float float_from_string(const char *string, char **error);
 Float float_from_hex(const char *string, char **error);
 Int128 i128_from_double(double x);

src/compiler/float.c

@@ -85,6 +85,12 @@ Float float_div(Float op1, Float op2)
 	return (Float){ op1.f / op2.f, op1.type };
 }
 
+Float float_rem(Float op1, Float op2)
+{
+	assert(op1.type == op2.type);
+	return (Float){fmod(op1.f, op2.f), op1.type };
+}
+
 Float float_neg(Float op)
 {
 	op.f = -op.f;

src/compiler/sema_expr.c

@@ -5561,19 +5561,36 @@ static bool sema_expr_analyse_mod(SemaContext *context, Expr *expr, Expr *left,
 	// 1. Analyse both sides and promote to a common type
 	if (!sema_binary_analyse_arithmetic_subexpr(context, expr, NULL, false)) return false;
 
-	// 3. a % 0 is not valid, so detect it.
-	if (expr_is_const(right) && int_is_zero(right->const_expr.ixx))
+	Type *flat = type_flatten(left->type);
+	if (type_is_float(flat))
 	{
-		SEMA_ERROR(right, "Cannot perform %% with a constant zero.");
-		return false;
-	}
+		// 3. a % 0 is not valid, so detect it.
+		if (expr_is_const(right) && right->const_expr.fxx.f == 0.0)
+		{
+			RETURN_SEMA_ERROR(right, "Cannot perform %% with a constant zero.");
+		}
 
-	// 4. Constant fold
-	if (expr_both_const(left, right) && sema_constant_fold_ops(left))
+		// 4. Constant fold
+		if (expr_both_const(left, right) && sema_constant_fold_ops(left))
+		{
+			expr_replace(expr, left);
+			// 4a. Remember this is remainder.
+			expr->const_expr.fxx = float_rem(left->const_expr.fxx, right->const_expr.fxx);
+		}
+	}
+	else
 	{
-		expr_replace(expr, left);
-		// 4a. Remember this is remainder.
-		expr->const_expr.ixx = int_rem(left->const_expr.ixx, right->const_expr.ixx);
+		assert(type_is_integer(flat));
+		// 3. a % 0 is not valid, so detect it.
+		if (expr_is_const(right) && int_is_zero(right->const_expr.ixx)) RETURN_SEMA_ERROR(right, "Cannot perform %% with a constant zero.");
+
+		// 4. Constant fold
+		if (expr_both_const(left, right) && sema_constant_fold_ops(left))
+		{
+			expr_replace(expr, left);
+			// 4a. Remember this is remainder.
+			expr->const_expr.ixx = int_rem(left->const_expr.ixx, right->const_expr.ixx);
+		}
 	}
 
 	expr->type = type_add_optional(left->type, IS_OPTIONAL(right));

test/test_suite/compile_time/mod_ct.c3t

@@ -0,0 +1,17 @@
+// #target: macos-x64
+module test;
+fn int main()
+{
+	double a = 4.5 % 5;
+	double b = -4.5 % 5;
+	int ai = 4 % 5;
+	int bi = -4 % 5;
+    return 0;
+}
+
+/* #expect: test.ll
+
+store double 4.500000e+00, ptr %a, align 8
+store double -4.500000e+00, ptr %b, align 8
+store i32 4, ptr %ai, align 4
+store i32 -4, ptr %bi, align 4