diff mbox series

[5/5] bitwise: early expansion of simple constants

Message ID 20220627190540.13358-6-luc.vanoostenryck@gmail.com (mailing list archive)
State New, archived
Headers show
Series allow -1 and compares in bitwise types | expand

Commit Message

Luc Van Oostenryck June 27, 2022, 7:05 p.m. UTC
C has only positive constants: -1 is really an expression,
the unary '-' operator applied to the constant 1. '-1' as
a constant value only exists after the expansion of constant
expressions.

This is rather unfortunate since it inhibits easy testing
of such constants in the evaluation phase, like here for
restricted_value().

So, expand expressions like +CTE, -CTE or ~CTE before
calling restricted_value().

Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
---
 evaluate.c                     | 48 +++++++++++++++++++++++++++++++++-
 validation/bitwise-cast.c      | 13 +++++++++
 validation/bitwise-is-signed.c |  1 -
 3 files changed, 60 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/evaluate.c b/evaluate.c
index bb8c0caa905a..33cc85c8d40f 100644
--- a/evaluate.c
+++ b/evaluate.c
@@ -413,11 +413,56 @@  static struct symbol *bad_expr_type(struct expression *expr)
 	return expr->ctype = &bad_ctype;
 }
 
+static bool expand_simple_constant(struct expression *expr, struct symbol *type)
+{
+	unsigned long long val, mask;
+	struct expression *pre;
+	struct symbol *ctype;
+	unsigned size;
+
+	if (expr->type != EXPR_PREOP)
+		return false;
+	pre = expr->unop;
+	if (pre->type != EXPR_VALUE)
+		return false;
+
+	ctype = pre->ctype;
+	if (!ctype || ctype != type)
+		return false;
+
+	size = ctype->bit_size;
+	if (!size)
+		return false;
+
+	mask = sign_bit(size);
+	switch (expr->op) {
+	case '+':
+		val = pre->value;
+		break;
+	case '-':
+		val = pre->value;
+		if (val == mask && !(ctype->ctype.modifiers & MOD_UNSIGNED))
+			return false;
+		val = -val;
+		break;
+	case '~':
+		val = pre->value;
+		val = ~val;
+		break;
+	default:
+		return false;
+	}
+	expr->op = 0;
+	expr->type = EXPR_VALUE;
+	expr->value = val & bits_mask(size);
+	return true;
+}
+
 static int restricted_value(struct expression *v, struct symbol *type)
 {
 	if (v->type != EXPR_VALUE)
 		return 1;
-	if (v->value != 0 && v->value != bits_mask(type->bit_size))
+	if (v->value != 0 && v->value != bits_mask(v->ctype->bit_size))
 		return 1;
 	return 0;
 }
@@ -1919,6 +1964,7 @@  Normal:
 	if (!(class & TYPE_FLOAT)) {
 		ctype = integer_promotion(ctype);
 		expr->unop = cast_to(expr->unop, ctype);
+		expand_simple_constant(expr, ctype);
 	} else if (expr->op != '~') {
 		/* no conversions needed */
 	} else {
diff --git a/validation/bitwise-cast.c b/validation/bitwise-cast.c
index 1075a3e9410c..01af56c73751 100644
--- a/validation/bitwise-cast.c
+++ b/validation/bitwise-cast.c
@@ -48,6 +48,19 @@  static __be32 bar1(void)
 	return (__be32)0xffffffff;
 }
 
+/* Implicit casts of minus one, legal */
+static __be32 foom(void)
+{
+	__be32 x = -1;
+	return x;
+}
+
+/* Explicit cast of minus one, legal */
+static __be32 barm(void)
+{
+	return (__be32)-1;
+}
+
 /*
  * check-name: conversions to bitwise types
  * check-command: sparse -Wbitwise $file
diff --git a/validation/bitwise-is-signed.c b/validation/bitwise-is-signed.c
index dd9c147173cd..99d16bd20f9b 100644
--- a/validation/bitwise-is-signed.c
+++ b/validation/bitwise-is-signed.c
@@ -15,7 +15,6 @@  int fou(void) { return !is_signed_type(u); }
 /*
  * check-name: bitwise-is-signed
  * check-command: test-linearize -Wno-decl $file
- * check-known-to-fail
  *
  * check-output-ignore
  * check-output-returns: 1