[PATCH v2 3/8] div0: warn on integer divide by 0 also when the lhs is not constant

[Luc Van Oostenryck <luc.vanoostenryck@gmail.com>]

The current code detects and warns on division by zero but
only when the left-hand side is a constant value.

Fix that by moving up the code which detect such divisions
before checking if the LHS is a constant.

Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
---
 expand.c                 |  8 ++----
 validation/div-by-zero.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 68 insertions(+), 6 deletions(-)
 create mode 100644 validation/div-by-zero.c

diff --git a/expand.c b/expand.c
index 5f908c971..0b528ea5a 100644
--- a/expand.c
+++ b/expand.c
@@ -181,6 +181,8 @@ static int simplify_int_binop(struct expression *expr, struct symbol *ctype)
 	if (right->type != EXPR_VALUE)
 		return 0;
 	r = right->value;
+	if (!r && (expr->op == '/' || expr->op == '%'))
+		goto Div;
 	if (expr->op == SPECIAL_LEFTSHIFT || expr->op == SPECIAL_RIGHTSHIFT) {
 		if (r >= ctype->bit_size) {
 			if (conservative)
@@ -235,28 +237,22 @@ static int simplify_int_binop(struct expression *expr, struct symbol *ctype)
 		break;
 
 	case SIGNED('/'):
-		if (!r)
-			goto Div;
 		if (l == mask && sr == -1)
 			goto Overflow;
 		v = sl / sr;
 		break;
 
 	case UNSIGNED('/'):
-		if (!r) goto Div;
 		v = l / r; 
 		break;
 
 	case SIGNED('%'):
-		if (!r)
-			goto Div;
 		if (l == mask && sr == -1)
 			goto Overflow;
 		v = sl % sr;
 		break;
 
 	case UNSIGNED('%'):
-		if (!r) goto Div;
 		v = l % r;
 		break;
 
diff --git a/validation/div-by-zero.c b/validation/div-by-zero.c
new file mode 100644
index 000000000..500ceb8eb
--- /dev/null
+++ b/validation/div-by-zero.c
@@ -0,0 +1,66 @@
+int  scdiv(int a) { return 2 / 0; }
+int iscdiv(int a) { return 2 / (int) 0; }
+int lscdiv(int a) { return 2 / (long) 0; }
+int uscdiv(int a) { return 2 / (unsigned int) 0; }
+
+int  svdiv(int a) { return a / 0; }
+int isvdiv(int a) { return a / (int) 0; }
+int lsvdiv(int a) { return a / (long) 0; }
+int usvdiv(int a) { return a / (unsigned int) 0; }
+
+int  scmod(int a) { return 2 % 0; }
+int iscmod(int a) { return 2 % (int) 0; }
+int lscmod(int a) { return 2 % (long) 0; }
+int uscmod(int a) { return 2 % (unsigned int) 0; }
+
+int  svmod(int a) { return a % 0; }
+int isvmod(int a) { return a % (int) 0; }
+int lsvmod(int a) { return a % (long) 0; }
+int usvmod(int a) { return a % (unsigned int) 0; }
+
+int xsvdiv(int a) { if (a && 0) return a / 0; return 0; }
+int asvdiv(int a) { return a /= 0; }
+int osvdiv(int a) { return a / (a && 0); }
+
+int xsvmod(int a) { if (a && 0) return a % 0; return 0; }
+int asvmod(int a) { return a %= 0; }
+int osvmod(int a) { return a % (a && 0); }
+
+int ysvdiv(int a) { if (a && 0) return a /= 0; return 0; }
+int ysvmod(int a) { if (a && 0) return a %= 0; return 0; }
+
+int zsvdiv(int a) { if (0 && (a /  0)) return 1; return 0; }
+int zsvmod(int a) { if (0 && (a /= 0)) return 1; return 0; }
+
+int wsvdiv(int a) { if (0) return a / 0; return 0; }
+int wsvmod(int a) { if (0) return a % 0; return 0; }
+int vsvdiv(int a) { if (0) return a /= 0; return 0; }
+int vsvmod(int a) { if (0) return a %= 0; return 0; }
+
+/*
+ * check-name: div-by-zero.c
+ * check-command: sparse -Wno-decl $file
+ *
+ * check-error-start
+div-by-zero.c:1:30: warning: division by zero
+div-by-zero.c:2:30: warning: division by zero
+div-by-zero.c:3:30: warning: division by zero
+div-by-zero.c:4:30: warning: division by zero
+div-by-zero.c:6:30: warning: division by zero
+div-by-zero.c:7:30: warning: division by zero
+div-by-zero.c:8:30: warning: division by zero
+div-by-zero.c:9:30: warning: division by zero
+div-by-zero.c:11:30: warning: division by zero
+div-by-zero.c:12:30: warning: division by zero
+div-by-zero.c:13:30: warning: division by zero
+div-by-zero.c:14:30: warning: division by zero
+div-by-zero.c:16:30: warning: division by zero
+div-by-zero.c:17:30: warning: division by zero
+div-by-zero.c:18:30: warning: division by zero
+div-by-zero.c:19:30: warning: division by zero
+div-by-zero.c:21:42: warning: division by zero
+div-by-zero.c:25:42: warning: division by zero
+div-by-zero.c:35:37: warning: division by zero
+div-by-zero.c:36:37: warning: division by zero
+ * check-error-end
+ */
-- 
2.13.0