On 04/22/2015 12:36 PM, Marek Polacek wrote:
Currently, we warn if the right operand of a shift expression is negative, or greater than or equal to the length in bits of the promoted left operand.But we don't warn when we see a left shift of a negative value. That is undefined behavior since C99 and I believe C++11, so this patch implements a new warning, -Wshift-negative-value, only active in C99/C++11. A bunch of tests needed tweaking; I find it scary that some vect tests are invoking UB. Bootstrapped/regtested on x86_64-linux, ok for trunk? 2015-04-22 Marek Polacek <pola...@redhat.com> PR c/65179 * c-common.c (c_fully_fold_internal): Warn when left shifting a negative value. * c.opt (Wshift-negative-value): New option. * c-typeck.c (build_binary_op): Warn when left shifting a negative value. * typeck.c (cp_build_binary_op): Warn when left shifting a negative value. * doc/invoke.texi: Document -Wshift-negative-value. * c-c++-common/Wshift-negative-value-1.c: New test. * c-c++-common/Wshift-negative-value-2.c: New test. * c-c++-common/torture/vector-shift2.c: Use -Wno-shift-negative-value. * gcc.dg/torture/vector-shift2.c: Likewise. * gcc.c-torture/execute/pr40386.c: Likewise. * gcc.dg/tree-ssa/vrp65.c: Likewise. * gcc.dg/tree-ssa/vrp66.c: Likewise. * gcc.dg/vect/vect-sdivmod-1.c: Likewise. * gcc.dg/vect/vect-shift-2-big-array.c: Likewise. * gcc.dg/vect/vect-shift-2.c: Likewise. * gcc.target/i386/pr31167.c: Likewise. * g++.dg/init/array11.C: Add dg-warning. * gcc.dg/c99-const-expr-7.c: Add dg-warning and dg-error.
OK. jeff
