[PATCH] PR c/19978 multiple overflow warnings

["Manuel LÃpez-IbÃÃez" <lopezibanez at gmail dot com>]

:ADDPATCH c/c++:

The following patch fixes PR c/19978: once an expression overflowed,
an extra overflow warning is given for each additional operator that
appears in the expression. This also affects unary operators in C++
but it seems no one noticed that.

With this patch overflow warnings are emitted only if the result of a
binary or unary operation has TREE_OVERFLOW set, but its operands did
not.

The testcases multiple-overflow-warn-* have been checked to fail with
current mainline.  I have also added overflow-warn-6.c  to test that
everything works fine when the result of an operator is
CONSTANT_CLASS_P and its operands are not.

Bootstrapped and regression tested with --enable-languages=all on
i686-pc-linux-gnu for mainline revision 119259.

The changes to tree.h have been pre-approved by Roger Sayle.


2006-12-09  Manuel Lopez-Ibanez <manu@gcc.gnu.org>

   PR c/19978
   * tree.h (TREE_OVERFLOW_P): New.
   * cp/semantics.c (finish_unary_op_expr): Warn only if result
overflowed and operands did not.
   * c-typeck.c (parser_build_unary_op): Likewise.
   (parser_build_binary_op): Likewise.
   (convert_for_assignment): Remove redundant overflow_warning.
   * c-common.c (overflow_warning): Don't check or set TREE_OVERFLOW.

testsuite/
2006-12-09  Manuel Lopez-Ibanez <manu@gcc.gnu.org>

   PR c/19978
   * gcc.dg/multiple-overflow-warn-1.c: New.
   * gcc.dg/multiple-overflow-warn-2.c: New.
   * gcc.dg/overflow-warn-6.c: New.
   * g++.dg/warn/multiple-overflow-warn-1.C: New.

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