On 6/2/2021 11:09 AM, Jakub Jelinek wrote:
Hi!
When building gcc targetting xtensa-linux, there are 2 warnings the PR
complains about:
../../gcc/dwarf2cfi.c: In function ‘void init_one_dwarf_reg_size(int,
machine_mode, rtx, machine_mode, init_one_dwarf_reg_state*)’:
../../gcc/dwarf2cfi.c:291:12: warning: comparison of integer expressions of
different signedness: ‘const unsigned int’ and ‘int’ [-Wsign-compare]
291 | if (rnum >= DWARF_FRAME_REGISTERS)
../../gcc/function.c: In function ‘void gen_call_used_regs_seq(rtx_insn*,
unsigned int)’:
../../gcc/function.c:5897:63: warning: comparison of unsigned expression in ‘<
0’ is always false [-Wtype-limits]
5897 | if (crtl->uses_only_leaf_regs && LEAF_REG_REMAP (regno) < 0)
which might during bootstrap or when configured with --enable-werror-always
be turned into errors.
The first one is the -Wsign-compare warning, in c-family we do:
2281 /* Do not warn if the signed quantity is an unsuffixed integer
2282 literal (or some static constant expression involving such
2283 literals or a conditional expression involving such literals)
2284 and it is non-negative. */
2285 if (tree_expr_nonnegative_warnv_p (sop, &ovf))
2286 /* OK */;
and so don't warn if that function determines the expression is
non-negative. But xtensa defines DWARF_FRAME_REGISTERS as
(16 + (something ? 0 : 1)) and that isn't handled by
tree_expr_nonnegative_warnv_p, VRP can handle it of course, but that is much
later.
The second chunk rewrites it into a form that tree_expr_nonnegative_warnv_p
can handle, in particular (something ? 16 : 16 + 1), where for COND_EXPRs
that function checks both the 2nd and 3rd operand of the ternary operator
and if both are nonnegative, returns true.
The other warning has been introduced fairly recently; LEAF_REG_REMAP is
currently used by 2 targets only, and is documented to yield -1 if a hard
reg number can't be remapped and the remapped register number otherwise.
That means that the type of the expression should be signed (otherwise -1
could never appear), and on SPARC indeed it is defined as
extern char leaf_reg_remap[];
#define LEAF_REG_REMAP(REGNO) (leaf_reg_remap[REGNO])
so unless the host is -funsigned-char by default it works fine.
I guess sparc.[ch] should be fixed to use signed char of leaf_reg_remap,
Eric?
The argument to LEAF_REG_REMAP is often unsigned int though, hard
register numbers are usually not negative, and thus the warning.
I think xtensa doesn't have 2G hard registers and so it is ok to just cast
it to int.
Verified just by making sure the warnings go away in a cross, ok for trunk?
2021-06-02 Jakub Jelinek <ja...@redhat.com>
PR target/100841
* config/xtensa/xtensa.h (LEAF_REG_REMAP): Cast REGNO to int to avoid
-Wtype-limits warnings.
(DWARF_FRAME_REGISTER): Rewrite into ternary operator with addition
in operands to avoid -Wsign-compare warnings.
OK.
jeff
