isel: Don't duplicate comparisons for -O0 nor -fno-tree-ter [PR116101]

isel: Don't duplicate comparisons for -O0 nor -fno-tree-ter [PR116101]

While doing cleanups on this code I noticed that we do the duplicate
of comparisons at -O0. For C and C++ code this makes no difference as
the gimplifier never produces COND_EXPR. But it could make a difference
for other front-ends.
Oh and for -fno-tree-ter, duplicating the comparison is just a waste
as it is never used for expand.

I also decided to add a few testcases so this is checked in the future.
Even added one for the duplication itself.

Bootstrapped and tested on x86_64-linux-gnu with no regressions.

	PR tree-optimization/116101

gcc/ChangeLog:

	* gimple-isel.cc (maybe_duplicate_comparison): Don't
	do anything for -O0 or -fno-tree-ter.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/dup_compare_cond-1.c: New test.
	* gcc.dg/tree-ssa/dup_compare_cond-2.c: New test.
	* gcc.dg/tree-ssa/dup_compare_cond-3.c: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>