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* [Bug preprocessor/55715] New: bogus overflow warning for #if A-B when A<0 & B==minimum integer
@ 2012-12-17 7:23 eggert at gnu dot org
2013-12-10 1:23 ` [Bug preprocessor/55715] " jsm28 at gcc dot gnu.org
2013-12-10 1:25 ` jsm28 at gcc dot gnu.org
0 siblings, 2 replies; 3+ messages in thread
From: eggert at gnu dot org @ 2012-12-17 7:23 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55715
Bug #: 55715
Summary: bogus overflow warning for #if A-B when A<0 &
B==minimum integer
Classification: Unclassified
Product: gcc
Version: 4.7.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: preprocessor
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: eggert@gnu.org
Consider this C program:
#if 9223372036854775807 < 0
#endif
#if -1 - 9223372036854775807 < 0
#endif
#if -1 - (-1 - 9223372036854775807) < 0
#endif
When compiled with GCC (x86-64), GCC 4.7.2 warns:
t.c:5:37: warning: integer overflow in preprocessor expression [enabled by
default]
The warning is incorrect, since there is no overflow in this program.
Evidently GCC's preprocessor computes A-B by first negating B, and then adding
the result to A. This causes GCC to incorrectly report overflow when B is the
minimum possible integer and A is negative, because in this case -B overflows
even though A-B does not overflow.
^ permalink raw reply [flat|nested] 3+ messages in thread* [Bug preprocessor/55715] bogus overflow warning for #if A-B when A<0 & B==minimum integer 2012-12-17 7:23 [Bug preprocessor/55715] New: bogus overflow warning for #if A-B when A<0 & B==minimum integer eggert at gnu dot org @ 2013-12-10 1:23 ` jsm28 at gcc dot gnu.org 2013-12-10 1:25 ` jsm28 at gcc dot gnu.org 1 sibling, 0 replies; 3+ messages in thread From: jsm28 at gcc dot gnu.org @ 2013-12-10 1:23 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55715 --- Comment #1 from Joseph S. Myers <jsm28 at gcc dot gnu.org> --- Author: jsm28 Date: Tue Dec 10 01:23:37 2013 New Revision: 205846 URL: http://gcc.gnu.org/viewcvs?rev=205846&root=gcc&view=rev Log: PR preprocessor/55715 libcpp: * expr.c (num_binary_op): Implement subtraction directly rather than with negation and falling through into addition case. gcc/testsuite: * gcc.dg/cpp/expr-overflow-1.c: New test. Added: trunk/gcc/testsuite/gcc.dg/cpp/expr-overflow-1.c Modified: trunk/gcc/testsuite/ChangeLog trunk/libcpp/ChangeLog trunk/libcpp/expr.c ^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug preprocessor/55715] bogus overflow warning for #if A-B when A<0 & B==minimum integer 2012-12-17 7:23 [Bug preprocessor/55715] New: bogus overflow warning for #if A-B when A<0 & B==minimum integer eggert at gnu dot org 2013-12-10 1:23 ` [Bug preprocessor/55715] " jsm28 at gcc dot gnu.org @ 2013-12-10 1:25 ` jsm28 at gcc dot gnu.org 1 sibling, 0 replies; 3+ messages in thread From: jsm28 at gcc dot gnu.org @ 2013-12-10 1:25 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55715 Joseph S. Myers <jsm28 at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution|--- |FIXED Target Milestone|--- |4.9.0 --- Comment #2 from Joseph S. Myers <jsm28 at gcc dot gnu.org> --- Fixed for 4.9. ^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2013-12-10 1:25 UTC | newest] Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2012-12-17 7:23 [Bug preprocessor/55715] New: bogus overflow warning for #if A-B when A<0 & B==minimum integer eggert at gnu dot org 2013-12-10 1:23 ` [Bug preprocessor/55715] " jsm28 at gcc dot gnu.org 2013-12-10 1:25 ` jsm28 at gcc dot gnu.org
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