scc

commit 2bc598101275d978b5494d034bd71d8e2b443f4a
parent c3dde9b82a4e46f51444725132ecd65c7bdeedbe
Author: Roberto E. Vargas Caballero <k0ga@shike2.net>
Date:   Mon, 23 Mar 2026 11:28:40 +0100

cc1: Don't reduce modulus in signed types

Reducing modulus to and  is valid only in types without sign,
because in case of having a sign the bitwise operation does
not consider the sign bit.

Diffstat:
M
src/cmd/scc-cc/cc1/fold.c
 | 
8
++++++--
A
tests/cc/execute/0249-mod.c
 | 
15
+++++++++++++++
M
tests/cc/execute/scc-tests.lst
 | 
1
+

3 files changed, 22 insertions(+), 2 deletions(-)
diff --git a/src/cmd/scc-cc/cc1/fold.c b/src/cmd/scc-cc/cc1/fold.c
@@ -797,6 +797,9 @@ reduce(Node *np)
 	Node *aux, *aux2;
 	int op = np->op;
 
+	if (np->type->prop & TSIGNED)
+		return;
+
 	switch (op) {
 	case OMOD:
 		/* i % 2^n => i & n-1 */
@@ -886,9 +889,10 @@ repeat:
 			associative(np);
 		}
 		np = fold(np);
-		if (!isfloat)
+		if (!isfloat) {
 			np = identity(np);
-		reduce(np);
+			reduce(np);
+		}
 		break;
 	}
 
diff --git a/tests/cc/execute/0249-mod.c b/tests/cc/execute/0249-mod.c
@@ -0,0 +1,15 @@
+int
+main(void)
+{
+	int a = -1;
+	unsigned b = 3, c = 10;
+
+	if (!(a % 2 == -1))
+		return 1;
+	if (!(b % 2 == 1))
+		return 2;
+	if (!(c % 8 == 2))
+		return 2;
+
+	return 0;
+}
diff --git a/tests/cc/execute/scc-tests.lst b/tests/cc/execute/scc-tests.lst
@@ -239,3 +239,4 @@
 0246-branch.c
 0247-float.c
 0248-enum.c
+0249-mod.c