libcpp: Fix up padding handling in funlike_invocation_p [PR104147]

As mentioned in the PR, in some cases we preprocess incorrectly when we
encounter an identifier which is defined as function-like macro, followed
by at least 2 CPP_PADDING tokens and then some other identifier.
On the following testcase, the problem is in the 3rd funlike_invocation_p,
the tokens are CPP_NAME Y, CPP_PADDING (the pfile->avoid_paste shared token),
CPP_PADDING (one created with padding_token, val.source is non-NULL and
val.source->flags & PREV_WHITE is non-zero) and then another CPP_NAME.
funlike_invocation_p remembers there was a padding token, but remembers the
first one because of its condition, then the next token is the CPP_NAME,
which is not CPP_OPEN_PAREN, so the CPP_NAME token is backed up, but as we
can't easily backup more tokens, it pushes into a new context the padding
token (the pfile->avoid_paste one).  The net effect is that when Y is not
defined as fun-like macro, we read Y, avoid_paste, padding_token, Y,
while if Y is fun-like macro, we read Y, avoid_paste, avoid_paste, Y
(the second avoid_paste is because that is how we handle end of a context).
Now, for stringify_arg that is unfortunately a significant difference,
which handles CPP_PADDING tokens with:
      if (token->type == CPP_PADDING)
        {
          if (source == NULL
              || (!(source->flags & PREV_WHITE)
                  && token->val.source == NULL))
            source = token->val.source;
          continue;
        }
and later on
      /* Leading white space?  */
      if (dest - 1 != BUFF_FRONT (pfile->u_buff))
        {
          if (source == NULL)
            source = token;
          if (source->flags & PREV_WHITE)
            *dest++ = ' ';
        }
      source = NULL;
(and c-ppoutput.cc has similar code).
So, when Y is not fun-like macro, ' ' is added because padding_token's
val.source->flags & PREV_WHITE is non-zero, while when it is fun-like
macro, we don't add ' ' in between, because source is NULL and so
used from the next token (CPP_NAME Y), which doesn't have PREV_WHITE set.

Now, the funlike_invocation_p condition
       if (padding == NULL
           || (!(padding->flags & PREV_WHITE) && token->val.source == NULL))
        padding = token;
looks very similar to that in stringify_arg/c-ppoutput.cc, so I assume
the intent was to prefer do the same thing and pick the right padding.
But there are significant differences.  Both stringify_arg and c-ppoutput.cc
don't remember the CPP_PADDING token, but its val.source instead, while
in funlike_invocation_p we want to remember the padding token that has the
significant information for stringify_arg/c-ppoutput.cc.
So, IMHO we want to overwrite padding if:
1) padding == NULL (remember that there was any padding at all)
2) padding->val.source == NULL (this matches the source == NULL
   case in stringify_arg)
3) !(padding->val.source->flags & PREV_WHITE) && token->val.source == NULL
   (this matches the !(source->flags & PREV_WHITE) && token->val.source == NULL
   case in stringify_arg)

2022-02-01  Jakub Jelinek  <jakub@redhat.com>

	PR preprocessor/104147
	* macro.cc (funlike_invocation_p): For padding prefer a token
	with val.source non-NULL especially if it has PREV_WHITE set
	on val.source->flags.  Add gcc_assert that CPP_PADDING tokens
	don't have PREV_WHITE set in flags.

	* c-c++-common/cpp/pr104147.c: New test.

diff --git a/gcc/testsuite/c-c++-common/cpp/pr104147.c b/gcc/testsuite/c-c++-common/cpp/pr104147.c
new file mode 100644 (file)
index 0000000..4ee237e
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/cpp/pr104147.c
@@ -0,0 +1,27 @@
+/* PR preprocessor/104147 */
+/* { dg-do run } */
+
+#define X(x,y)         x y
+#define STR_(x) #x
+#define STR(x)         STR_(x)
+const char *str =
+STR(X(Y,Y))
+#define Y()
+STR(X(Y,Y))
+#undef Y
+STR(X(Y,Y))
+#define Y()
+STR(X(Y,Y))
+STR(X(Y,
+Y))
+STR(X(Y
+,Y))
+;
+
+int
+main ()
+{
+  if (__builtin_strcmp (str, "Y YY YY YY YY YY Y") != 0)
+    __builtin_abort ();
+  return 0;
+}

diff --git a/libcpp/macro.cc b/libcpp/macro.cc
index 65b7a1c..8ebf360 100644 (file)
--- a/libcpp/macro.cc
+++ b/libcpp/macro.cc
@@ -1373,8 +1373,11 @@ funlike_invocation_p (cpp_reader *pfile, cpp_hashnode *node,
       token = cpp_get_token (pfile);
       if (token->type != CPP_PADDING)
        break;
+      gcc_assert ((token->flags & PREV_WHITE) == 0);
       if (padding == NULL
-         || (!(padding->flags & PREV_WHITE) && token->val.source == NULL))
+         || padding->val.source == NULL
+         || (!(padding->val.source->flags & PREV_WHITE)
+             && token->val.source == NULL))
        padding = token;
     }