Fix expansion of `(a & 2) != 1`

I had a thinko in r14-1600-ge60593f3881c72a96a3fa4844d73e8a2cd14f670
where we would remove the `& CST` part if we ended up not calling
expand_single_bit_test.
This fixes the problem by introducing a new variable that will be used
for calling expand_single_bit_test.
As afar as I know this can only show up when disabling optimization
passes as this above form would have been optimized away.

Committed as obvious after a bootstrap/test on x86_64-linux-gnu.

	PR middle-end/111863

gcc/ChangeLog:

	* expr.cc (do_store_flag): Don't over write arg0
	when stripping off `& POW2`.

gcc/testsuite/ChangeLog:

	* gcc.c-torture/execute/pr111863-1.c: New test.

1 files changed, 16 insertions, 0 deletions

diff --git a/gcc/testsuite/gcc.c-torture/execute/pr111863-1.c b/gcc/testsuite/gcc.c-torture/execute/pr111863-1.c
new file mode 100644
index 0000000..4e27fe6
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr111863-1.c
@@ -0,0 +1,16 @@
+/* { dg-options " -fno-tree-ccp -fno-tree-dominator-opts -fno-tree-vrp" } */
+
+__attribute__((noipa))
+int f(int a)
+{
+        a &= 2;
+        return a != 1;
+}
+int main(void)
+{
+        int t = f(1);
+        if (!t)
+        __builtin_abort();
+        __builtin_printf("%d\n",t);
+        return 0;
+}