forwprop: Handle already true/false branchs in optimize_unreachable [PR122588]

When optimize_unreachable was moved from fab to forwprop, I missed that due to
the integrated copy prop, we might end up with an already true branch leading
to a __builtin_unreachable block. optimize_unreachable would switch around
the if and things go down hill from there since the other edge was already
marked as non-executable, forwprop didn't process those blocks and didn't
do copy prop into that block and the original assignment statement was removed.

This fixes the problem by having optimize_unreachable not touch the if
statement was already changed to true/false.

Note I placed the testcase in gcc.c-torture/compile as gcc.dg/torture
is NOT currently testing -Og (see PR 122450 for that).

Changes since v1:
 * v2: Add gimple testcase.

Bootstrapped and tested on x86_64-linux-gnu.

	PR tree-optimization/122588

gcc/ChangeLog:

	* tree-ssa-forwprop.cc (optimize_unreachable): Don't touch
	if the condition was already true or false.

gcc/testsuite/ChangeLog:

	* gcc.c-torture/compile/pr122588-1.c: New test.
	* gcc.dg/tree-ssa/pr122588-1.c: New test.

Signed-off-by: Andrew Pinski <andrew.pinski@oss.qualcomm.com>

0 files changed, 0 insertions, 0 deletions