https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96788
Pascal Cuoq <pascal_cuoq at hotmail dot com> changed:
What |Removed |Added
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CC| |pascal_cuoq at hotmail dot com
--- Comment #6 from Pascal Cuoq <pascal_cuoq at hotmail dot com> ---
Joseph Myers wrote:
> The warnings are attempting to cover both the C90
> case where a decimal constant too large for signed long can be unsigned
> long, and the case of a constant too large for intmax_t.
In the case of the constant 10000000000000000000, each of the two kind of
warnings, “ integer constant is so large that it is unsigned” and “this decimal
constant is unsigned only in ISO C90” can be misleading.
Consider the compilation unit:
int x;
void f(void) {
x = -10000000000000000000 < 0;
}
1/ Misleading warning “this decimal constant is unsigned only in ISO C90”
Compiler Explorer link: https://gcc.godbolt.org/z/4Eze1f
Using GCC 10.2 targeting x86, the compilation options “-O -m32 -std=c89” make
GCC compile f as below, and emit the warning “this decimal constant is unsigned
only in ISO C90”
f:
movl $0, x
ret
Actually, changing the C dialect to C99 does not make the constant not
unsigned, since GCC emits the same assembly code for f (setting x to 0) with
“-O -m32 -std=c99”
2/ Misleading warning “integer constant is so large that it is unsigned”
Compiler Explorer link: https://gcc.godbolt.org/z/MGjn5G
Using GCC 10.2 targeting x86, the compilation options “-O -m64 -std=c99” make
GCC compile f as below, and emit the warning “integer constant is so large that
it is unsigned”.
f:
movl $1, x(%rip)
ret
The constant is not unsigned. If it were, the function f would not set x to 1.
