PR c++/55095
	* c-common.c (c_fully_fold_internal): Warn about left shift overflows.
	Use EXPR_LOC_OR_LOC.
	(maybe_warn_shift_overflow): New function.
	* c-common.h (maybe_warn_shift_overflow): Declare.
	* c-opts.c (c_common_post_options): Set warn_shift_overflow.
	* c.opt (Wshift-overflow): New option.

	* c-typeck.c (digest_init): Pass OPT_Wpedantic to pedwarn_init.
	(build_binary_op): Warn about left shift overflows.

	* typeck.c (cp_build_binary_op): Warn about left shift overflows.

	* doc/invoke.texi: Document -Wshift-overflow and -Wshift-overflow=.

	* c-c++-common/Wshift-overflow-1.c: New test.
	* c-c++-common/Wshift-overflow-2.c: New test.
	* c-c++-common/Wshift-overflow-3.c: New test.
	* c-c++-common/Wshift-overflow-4.c: New test.
	* c-c++-common/Wshift-overflow-5.c: New test.
	* g++.dg/cpp1y/left-shift-1.C: New test.
	* gcc.dg/c90-left-shift-2.c: New test.
	* gcc.dg/c90-left-shift-3.c: New test.
	* gcc.dg/c99-left-shift-2.c: New test.
	* gcc.dg/c99-left-shift-3.c: New test.
	* gcc.dg/pr40501.c: Use -Wno-shift-overflow.
	* gcc.c-torture/execute/pr40386.c: Likewise.
	* gcc.dg/vect/pr33373.c: Likewise.
	* gcc.dg/vect/vect-shift-2-big-array.c: Likewise.
	* gcc.dg/vect/vect-shift-2.c: Likewise.

Co-Authored-By: Richard Sandiford <richard.sandiford@arm.com>

From-SVN: r225998