DSE: Fix ICE after allow vector type in get_stored_val

We allowed vector type for get_stored_val when read is less than or
equal to store in previous.  Unfortunately,  the valididate_subreg
treats the vector type's size is less than vector register as
invalid.  Then we will have ICE here.

This patch would like to fix it by filter-out the invalid type size,
and make sure the subreg is valid for both the read_mode and store_mode
before perform the real gen_lowpart.

The below test suites are passed for this patch:

* The x86 bootstrap test.
* The x86 regression test.
* The riscv rv64gcv regression test.
* The riscv rv64gc regression test.
* The aarch64 regression test.

gcc/ChangeLog:

	* dse.cc (get_stored_val): Make sure read_mode/write_mode
	is valid subreg before gen_lowpart.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/base/bug-6.c: New test.

Signed-off-by: Pan Li <pan2.li@intel.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/gcc/dse.cc b/gcc/dse.cc
index edc7a1d..1596da9 100644
--- a/gcc/dse.cc
+++ b/gcc/dse.cc
@@ -1946,7 +1946,9 @@ get_stored_val (store_info *store_info, machine_mode read_mode,
 				 copy_rtx (store_info->const_rhs));
   else if (VECTOR_MODE_P (read_mode) && VECTOR_MODE_P (store_mode)
     && known_le (GET_MODE_BITSIZE (read_mode), GET_MODE_BITSIZE (store_mode))
-    && targetm.modes_tieable_p (read_mode, store_mode))
+    && targetm.modes_tieable_p (read_mode, store_mode)
+    && validate_subreg (read_mode, store_mode, copy_rtx (store_info->rhs),
+			subreg_lowpart_offset (read_mode, store_mode)))
     read_reg = gen_lowpart (read_mode, copy_rtx (store_info->rhs));
   else
     read_reg = extract_low_bits (read_mode, store_mode,