[PATCH] libcpp: Fix up padding handling in funlike_invocation_p [PR104147]

[Jakub Jelinek <jakub@redhat.com>]

Hi!

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)

Bootstrapped/regtested on powerpc64le-linux, ok for trunk
(and after a while for some release branches)?

2022-01-31  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.

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

--- libcpp/macro.cc.jj	2022-01-18 11:59:00.277972128 +0100
+++ libcpp/macro.cc	2022-01-31 15:44:49.208847524 +0100
@@ -1374,7 +1374,9 @@ funlike_invocation_p (cpp_reader *pfile,
       if (token->type != CPP_PADDING)
 	break;
       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;
     }
 
--- gcc/testsuite/c-c++-common/cpp/pr104147.c.jj	2022-01-31 15:54:18.113847934 +0100
+++ gcc/testsuite/c-c++-common/cpp/pr104147.c	2022-01-31 15:54:04.530038941 +0100
@@ -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;
+}

	Jakub