In this PR the testcase ICEs because a BIT_INSERT_EXPR whose replaced bits are
not fully inside the container is generated. A size check is added to avoid
this kind of ICE.

gcc/ChangeLog:

	PR tree-optimization/94574
	* tree-ssa.c (non_rewritable_lvalue_p): Add size check when analyzing
	whether a vector-insert is rewritable using a BIT_INSERT_EXPR.

gcc/testsuite/ChangeLog:

	PR tree-optimization/94574
	* gcc.dg/pr94574.c: New test.