re PR c/80116 (Warn about macros expanding to multiple statements)

	PR c/80116
	* c-common.h (warn_for_multistatement_macros): Declare.
	* c-warn.c: Include "c-family/c-indentation.h".
	(warn_for_multistatement_macros): New function.
	* c.opt (Wmultistatement-macros): New option.
	* c-indentation.c (guard_tinfo_to_string): No longer static.
	Change the parameter type to "enum rid".  Handle RID_SWITCH.
	* c-indentation.h (guard_tinfo_to_string): Declare.

	* c-parser.c (c_parser_if_body): Set the location of the
	body of the conditional after parsing all the labels.  Call
	warn_for_multistatement_macros.
	(c_parser_else_body): Likewise.
	(c_parser_switch_statement): Likewise.
	(c_parser_while_statement): Likewise.
	(c_parser_for_statement): Likewise.
	(c_parser_statement): Add a default argument.  Save the location
	after labels have been parsed.
	(c_parser_c99_block_statement): Likewise.

	* parser.c (cp_parser_statement): Add a default argument.  Save the
	location of the expression-statement after labels have been parsed.
	(cp_parser_implicitly_scoped_statement): Set the location of the
	body of the conditional after parsing all the labels.  Call
	warn_for_multistatement_macros.
	(cp_parser_already_scoped_statement): Likewise.

	* doc/invoke.texi: Document -Wmultistatement-macros.

	* c-c++-common/Wmultistatement-macros-1.c: New test.
	* c-c++-common/Wmultistatement-macros-2.c: New test.
	* c-c++-common/Wmultistatement-macros-3.c: New test.
	* c-c++-common/Wmultistatement-macros-4.c: New test.
	* c-c++-common/Wmultistatement-macros-5.c: New test.
	* c-c++-common/Wmultistatement-macros-6.c: New test.
	* c-c++-common/Wmultistatement-macros-7.c: New test.
	* c-c++-common/Wmultistatement-macros-8.c: New test.
	* c-c++-common/Wmultistatement-macros-9.c: New test.
	* c-c++-common/Wmultistatement-macros-10.c: New test.
	* c-c++-common/Wmultistatement-macros-11.c: New test.

From-SVN: r249643

1 files changed, 28 insertions, 1 deletions

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index e4ca1b4..d1e097b 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -294,7 +294,7 @@ Objective-C and Objective-C++ Dialects}.
 -Wmain  -Wmaybe-uninitialized  -Wmemset-elt-size  -Wmemset-transposed-args @gol
 -Wmisleading-indentation  -Wmissing-braces @gol
 -Wmissing-field-initializers  -Wmissing-include-dirs @gol
--Wno-multichar  -Wnonnull  -Wnonnull-compare @gol
+-Wno-multichar  -Wmultistatement-macros  -Wnonnull  -Wnonnull-compare @gol
 -Wnormalized=@r{[}none@r{|}id@r{|}nfc@r{|}nfkc@r{]} @gol
 -Wnull-dereference  -Wodr  -Wno-overflow  -Wopenmp-simd  @gol
 -Woverride-init-side-effects  -Woverlength-strings @gol
@@ -3842,6 +3842,7 @@ Options} and @ref{Objective-C and Objective-C++ Dialect Options}.
 -Wmemset-transposed-args @gol
 -Wmisleading-indentation @r{(only for C/C++)} @gol
 -Wmissing-braces @r{(only for C/ObjC)} @gol
+-Wmultistatement-macros  @gol
 -Wnarrowing @r{(only for C++)}  @gol
 -Wnonnull  @gol
 -Wnonnull-compare  @gol
@@ -4514,6 +4515,32 @@ This warning is enabled by @option{-Wall}.
 @opindex Wno-missing-include-dirs
 Warn if a user-supplied include directory does not exist.
 
+@item -Wmultistatement-macros
+@opindex Wmultistatement-macros
+@opindex Wno-multistatement-macros
+Warn about unsafe multiple statement macros that appear to be guarded
+by a clause such as @code{if}, @code{else}, @code{for}, @code{switch}, or
+@code{while}, in which only the first statement is actually guarded after
+the macro is expanded.
+
+For example:
+
+@smallexample
+#define DOIT x++; y++
+if (c)
+  DOIT;
+@end smallexample
+
+will increment @code{y} unconditionally, not just when @code{c} holds.
+The can usually be fixed by wrapping the macro in a do-while loop:
+@smallexample
+#define DOIT do @{ x++; y++; @} while (0)
+if (c)
+  DOIT;
+@end smallexample
+
+This warning is enabled by @option{-Wall} in C and C++.
+
 @item -Wparentheses
 @opindex Wparentheses
 @opindex Wno-parentheses