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cpplib: expression parser
- To: gcc-patches at gcc dot gnu dot org
- Subject: cpplib: expression parser
- From: Neil Booth <NeilB at earthling dot net>
- Date: Fri, 31 Mar 2000 20:29:27 +0900
- Cc: Zack Weinberg <zack at wolery dot cumb dot org>, Jonathan Larmour <jlarmour at redhat dot co dot uk>
This is the first of a set of patches to the preprocessor's expression
parser. The ultimate goal is to make the code a little clearer and
faster, and to improve the quality of the error messages.
This patch fixes the following bugs:-
o "#if" by itself without an expression was accepted.
o "#if (2" produced an internal compiler error.
o "#if 1 ? 1 ? 2 : 2 : 1" produced a "':' without '?'" error.
o "#if 1 + + + 1" was accepted.
o Now I understand the algorithm better, the correct fix to the bug
Jonathan reported a couple of weeks ago:
#if 16 * (1) + 4 == 20
now evaluates to true rather than false, because the '+' is
correctly interpreted as a binary operator.
A bit later I'll add a series of test suites for cpplib's expression
parser based on those I'm using for testing, which should exercise
most operator-combination possibilities.
gcc bootstraps with this. OK to commit?
Neil.
* cppexp.c: Delete SKIP_OPERAND. Correct priority
PAREN_INNER_PRIO.
(_cpp_parse_expr): Check for multiple unary +/- operators.
Correct priorities of ':' and '?'. Treat ')' as having a
value. Ensure conditional expression is not void.
Index: gcc/cppexp.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/cppexp.c,v
retrieving revision 1.39
diff -u -p -r1.39 cppexp.c
--- cppexp.c 2000/03/13 22:01:06 1.39
+++ cppexp.c 2000/03/31 10:37:32
@@ -103,13 +103,6 @@ static struct operation lex PARAMS ((cpp
#define INT 309
#define CHAR 310
-#define LEFT_OPERAND_REQUIRED 1
-#define RIGHT_OPERAND_REQUIRED 2
-#define HAVE_VALUE 4
-/* SKIP_OPERAND is set for '&&' '||' '?' and ':' when the
- following operand should be short-circuited instead of evaluated. */
-#define SKIP_OPERAND 8
-
struct operation
{
short op;
@@ -644,7 +637,7 @@ right_shift (pfile, a, unsignedp, b)
}
/* These priorities are all even, so we can handle associatively. */
-#define PAREN_INNER_PRIO 0
+#define PAREN_INNER_PRIO 2
#define COMMA_PRIO 4
#define COND_PRIO (COMMA_PRIO+2)
#define OROR_PRIO (COND_PRIO+2)
@@ -660,6 +653,11 @@ right_shift (pfile, a, unsignedp, b)
#define UNARY_PRIO (MUL_PRIO+2)
#define PAREN_OUTER_PRIO (UNARY_PRIO+2)
+#define LEFT_OPERAND_REQUIRED 1
+#define RIGHT_OPERAND_REQUIRED 2
+#define HAVE_VALUE 4
+#define SIGN_QUALIFIED 8
+
#define COMPARE(OP) \
top->unsignedp = 0;\
top->value = (unsigned1 || unsigned2) \
@@ -722,9 +720,15 @@ _cpp_parse_expr (pfile)
lprio = PLUS_PRIO;
goto binop;
}
+ if (top->flags & SIGN_QUALIFIED)
+ {
+ cpp_error (pfile, "more than one sign operator given");
+ goto syntax_error;
+ }
+ flags = SIGN_QUALIFIED;
/* else fall through */
case '!': case '~':
- flags = RIGHT_OPERAND_REQUIRED;
+ flags |= RIGHT_OPERAND_REQUIRED;
rprio = UNARY_PRIO; lprio = rprio + 1; goto maybe_reduce;
case '*': case '/': case '%':
lprio = MUL_PRIO; goto binop;
@@ -746,12 +750,13 @@ _cpp_parse_expr (pfile)
goto maybe_reduce;
case ')':
lprio = PAREN_INNER_PRIO; rprio = PAREN_OUTER_PRIO;
+ flags = HAVE_VALUE; /* At least, we will have after reduction. */
goto maybe_reduce;
case ':':
- lprio = COND_PRIO; rprio = COND_PRIO;
+ lprio = COND_PRIO; rprio = COND_PRIO + 1;
goto maybe_reduce;
case '?':
- lprio = COND_PRIO + 1; rprio = COND_PRIO;
+ lprio = COND_PRIO; rprio = COND_PRIO;
goto maybe_reduce;
case ERROR:
goto syntax_error;
@@ -974,8 +979,7 @@ _cpp_parse_expr (pfile)
}
break;
case ')':
- if ((top[1].flags & HAVE_VALUE)
- || ! (top[0].flags & HAVE_VALUE)
+ if (! (top[0].flags & HAVE_VALUE)
|| top[0].op != '('
|| (top[-1].flags & HAVE_VALUE))
{
@@ -1002,6 +1006,8 @@ _cpp_parse_expr (pfile)
{
if (top != stack)
cpp_ice (pfile, "unbalanced stack in #if expression");
+ if (!(top->flags & HAVE_VALUE))
+ cpp_error (pfile, "#if with no expression");
result = (top->value != 0);
goto done;
}