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'-fdiagnostics-show-context[=DEPTH]'
'-fno-diagnostics-show-context'
With this option, the compiler might print the interesting control
flow chain that guards the basic block of the statement which has
the warning. DEPTH is the maximum depth of the control flow chain.
Currently, The list of the impacted warning options includes:
'-Warray-bounds', '-Wstringop-overflow', '-Wstringop-overread',
'-Wstringop-truncation'. and '-Wrestrict'. More warning options
might be added to this list in future releases. The forms
'-fdiagnostics-show-context' and '-fno-diagnostics-show-context'
are aliases for '-fdiagnostics-show-context=1' and
'-fdiagnostics-show-context=0', respectively.
For example:
$ cat t.c
extern void warn(void);
static inline void assign(int val, int *regs, int *index)
{
if (*index >= 4)
warn();
*regs = val;
}
struct nums {int vals[4];};
void sparx5_set (int *ptr, struct nums *sg, int index)
{
int *val = &sg->vals[index];
assign(0, ptr, &index);
assign(*val, ptr, &index);
}
$ gcc -Wall -O2 -c -o t.o t.c
t.c: In function ‘sparx5_set’:
t.c:12:23: warning: array subscript 4 is above array bounds of ‘int[4]’ [-Warray-bounds=]
12 | int *val = &sg->vals[index];
| ~~~~~~~~^~~~~~~
t.c:8:18: note: while referencing ‘vals’
8 | struct nums {int vals[4];};
| ^~~~
In the above, Although the warning is correct in theory, the warning message
itself is confusing to the end-user since there is information that cannot
be connected to the source code directly.
It will be a nice improvement to add more information in the warning message
to report where such index value come from.
With the new option -fdiagnostics-show-context=1, the warning message for
the above testing case is now:
$ gcc -Wall -O2 -fdiagnostics-show-context=1 -c -o t.o t.c
t.c: In function ‘sparx5_set’:
t.c:12:23: warning: array subscript 4 is above array bounds of ‘int[4]’ [-Warray-bounds=]
12 | int *val = &sg->vals[index];
| ~~~~~~~~^~~~~~~
‘sparx5_set’: events 1-2
4 | if (*index >= 4)
| ^
| |
| (1) when the condition is evaluated to true
......
12 | int *val = &sg->vals[index];
| ~~~~~~~~~~~~~~~
| |
| (2) warning happens here
t.c:8:18: note: while referencing ‘vals’
8 | struct nums {int vals[4];};
| ^~~~
PR tree-optimization/109071
PR tree-optimization/85788
PR tree-optimization/88771
PR tree-optimization/106762
PR tree-optimization/108770
PR tree-optimization/115274
PR tree-optimization/117179
gcc/ChangeLog:
* Makefile.in (OBJS): Add diagnostic-context-rich-location.o.
* common.opt (fdiagnostics-show-context): New option.
(fdiagnostics-show-context=): New option.
* diagnostic-context-rich-location.cc: New file.
* diagnostic-context-rich-location.h: New file.
* doc/invoke.texi (fdiagnostics-details): Add
documentation for the new options.
* gimple-array-bounds.cc (check_out_of_bounds_and_warn): Add
one new parameter. Use rich location with details for warning_at.
(array_bounds_checker::check_array_ref): Use rich location with
ditails for warning_at.
(array_bounds_checker::check_mem_ref): Add one new parameter.
Use rich location with details for warning_at.
(array_bounds_checker::check_addr_expr): Use rich location with
move_history_diagnostic_path for warning_at.
(array_bounds_checker::check_array_bounds): Call check_mem_ref with
one more parameter.
* gimple-array-bounds.h: Update prototype for check_mem_ref.
* gimple-ssa-warn-access.cc (warn_string_no_nul): Use rich location
with details for warning_at.
(maybe_warn_nonstring_arg): Likewise.
(maybe_warn_for_bound): Likewise.
(warn_for_access): Likewise.
(check_access): Likewise.
(pass_waccess::check_strncat): Likewise.
(pass_waccess::maybe_check_access_sizes): Likewise.
* gimple-ssa-warn-restrict.cc (pass_wrestrict::execute): Calculate
dominance info for diagnostics show context.
(maybe_diag_overlap): Use rich location with details for warning_at.
(maybe_diag_access_bounds): Use rich location with details for
warning_at.
gcc/testsuite/ChangeLog:
* gcc.dg/pr109071.c: New test.
* gcc.dg/pr109071_1.c: New test.
* gcc.dg/pr109071_10.c: New test.
* gcc.dg/pr109071_11.c: New test.
* gcc.dg/pr109071_12.c: New test.
* gcc.dg/pr109071_2.c: New test.
* gcc.dg/pr109071_3.c: New test.
* gcc.dg/pr109071_4.c: New test.
* gcc.dg/pr109071_5.c: New test.
* gcc.dg/pr109071_6.c: New test.
* gcc.dg/pr109071_7.c: New test.
* gcc.dg/pr109071_8.c: New test.
* gcc.dg/pr109071_9.c: New test.
* gcc.dg/pr117375.c: New test.
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