Re: [PATCH 1/3] Fold __builtin_str{n}{case}cmp functions (version 2)

["Martin Liška" <mliska@suse.cz>]

On 10/07/2016 12:50 PM, Richard Biener wrote:
> On Fri, Oct 7, 2016 at 10:39 AM, Martin Liška <mliska@suse.cz> wrote:
>> I'm resending the patch, where I implemented all builtins mentions in subject
>> in gimp-fold.c.
>>
>> Patch can bootstrap on ppc64le-redhat-linux and survives regression tests.
>>
>> Ready to be installed?
> 
> +       case BUILT_IN_STRNCASECMP:
> +         {
> +           r = strncmp (p1, p2, length);
> +           if (r == 0)
> +             known_result = true;
> 
> length might be -1 here -- I think you need to guard against that (but you can
> handle BUILT_IN_STRCASECMP which you miss?).  Likewise for the strncmp case.

Fixed, I've added comment to STRCASECMP case.

> 
> Also do we know whether the c_getstr () result is '\0'-terminated?  AFAICS these
> constant foldings were not implemented in builtins.c, I see a STRCMP one in
> fold-const-call.c though.  I believe the STRING_CST string is not guaranteed to
> be '\0' terminated (STRING_CST comes with explicit length).

You are absolutely right that we do not have always '\0'-terminated string constants.
Thus I'll send a patch that would return a string from c_getstr just in case
string[string_length] == 0 (separate email with patch will be sent).

> 
> +      tree temp = fold_build2_loc (loc, MEM_REF, cst_uchar_node, str1,
> +                                  off0);
> +      temp = gimple_build (&stmts, loc, NOP_EXPR, cst_uchar_node, temp);
> 
> please don't use gimple_build here, there is nothing to simplify for it.  Using
> a NOP_EXPR is also confusing (to match the API...).  Just do
> gimple_build_assign (make_ssa_name (...), ..) like other folders do.
> 
> +      replace_call_with_value (gsi, fold_convert_loc (loc, type, temp));
> 
> and you'd want to replace the call with the MEM_REF stmt using
> gsi_replace_with_seq_vops as you fail to set virtual operands properly
> above (thus you'll get ICEs when this only matches during GIMPLE opts).
> 
> +  location_t loc = gimple_location (stmt);
> +  tree cst_uchar_node = build_type_variant (unsigned_char_type_node, 1, 0);
> +  tree cst_uchar_ptr_node
> +    = build_pointer_type_for_mode (cst_uchar_node, ptr_mode, true);
> +  tree off0 = build_int_cst (cst_uchar_ptr_node, 0);
> 
> it would be nice to not do this tree building if nothign is folded.
> 
> +    case BUILT_IN_STRCMP:
> +      return gimple_fold_builtin_string_compare (gsi);
> +    case BUILT_IN_STRCASECMP:
> +      return gimple_fold_builtin_string_compare (gsi);
> +    case BUILT_IN_STRNCMP:
> +      return gimple_fold_builtin_string_compare (gsi);
> +    case BUILT_IN_STRNCASECMP:
> +      return gimple_fold_builtin_string_compare (gsi);
> 
> please do
> 
> +    case BUILT_IN_STRCMP:
> +    case BUILT_IN_STRCASECMP:
> ...
> +      return gimple_fold_builtin_string_compare (gsi);
> 
> Thanks,
> Richard.

Sure, all notes will be fixed in an email which reply to this one.

Martin

> 
>> Martin