https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80202
Bug ID: 80202
Summary: Spurious warning "array subscript is below array
bounds" with if-statement and char to unsigned int
conversion
Product: gcc
Version: 6.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: mchtly at gmail dot com
Target Milestone: ---
When compiling the following example with "g++ -Warray-bounds -O2", I get
spurious warnings:
// This type doesn't matter.
#define T int
T ac[2]; // No warning if this is static.
void foo(T); // No warning if this is defined.
enum {
ACM0 = 1, // This value must be greater than zero.
ACM1 // This value may be any non-negative integer.
};
// The parameter to srs() must be unsigned, the parameter to read()
// must be signed, and the first must be smaller than the second.
static_assert(sizeof(unsigned char) < sizeof(int), "");
T read(int reg) {
switch (reg) {
// No warning if either case statement is removed. Additional cases
// may be added anywhere.
case ACM0:
case ACM1:
return ac[reg - ACM0];
// The default case statement may be removed, and is only included
// for completeness.
default:
return 0;
}
}
void srs(unsigned char reg) {
if (reg < ACM0)
// Warning only if the return value of read() is passed to foo()
// at some point.
foo(read(reg));
}
And the output from GCC is:
$ g++ -c test.cpp -Warray-bounds -O2
test.cpp: In function 'void srs(unsigned char)':
test.cpp:22:25: warning: array subscript is below array bounds [-Warray-bounds]
return ac[reg - ACM0];
~~~~~~~~~~~~~^
