Re: [PATCH] xtensa: Fix 2 warnings during xtensa build [PR100841]

[Jeff Law <jeffreyalaw@gmail.com>]

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  <jakub@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