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

Richard Biener richard.guenther@gmail.com
Fri Oct 7 10:50:00 GMT 2016

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?

+         {
+           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.

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).

+      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);
+      return gimple_fold_builtin_string_compare (gsi);
+      return gimple_fold_builtin_string_compare (gsi);
+      return gimple_fold_builtin_string_compare (gsi);

please do

+    case BUILT_IN_STRCMP:
+      return gimple_fold_builtin_string_compare (gsi);


> Martin

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