[PATCH] middle-end: skipp stepped vector test of poly_int (1, 1) and allow the machine_mode definition with poly_uint16 (1, 1)

[juzhe.zhong@rivai.ai]

From: zhongjuzhe <juzhe.zhong@rivai.ai>

Hello. This patch is preparing for following RVV support.

Both ARM SVE and RVV (RISC-V 'V' Extension) support length-agnostic vector.
The minimum vector length of ARM SVE is 128-bit and the runtime invariant of ARM SVE is always 128-bit blocks.
However, the minimum vector length of RVV can be 32bit in 'Zve32*' sub-extension and 64bit in 'Zve*' sub-extension.

So I define the machine_mode as follows:
VECTOR_MODE_WITH_PREFIX (VNx, INT, DI, 1, 0);
ADJUST_NUNITS (MODE, riscv_vector_chunks);
The riscv_vector_chunks = poly_uint16 (1, 1)

The compilation is failed for the stepped vector test:
(const_vector:VNx1DI repeat [
        (const_int 8 [0x8])
        (const_int 7 [0x7])
    ])

I understand for stepped vector should always have aleast 2 elements and stepped vector initialization is common
for VLA (vector-lengthe agnostic) auto-vectorization. It makes sense that report fail for stepped vector of poly_uint16 (1, 1).

machine mode with nunits = poly_uint16 (1, 1) needs to implemented in intrinsics. And I would like to enable RVV auto-vectorization
with vector mode only nunits is larger than poly_uint16 (2, 2) in RISC-V backend. I think it will not create issue if we define
vector mode with nunits = poly_uint16 (1, 1). Feel free to correct me or offer me some other better solutions. Thanks!

  

gcc/ChangeLog:

        * simplify-rtx.cc (test_vector_subregs_fore_back): skip test for poly_uint16 (1, 1).

---
 gcc/simplify-rtx.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc
index 7d09bf7103d..61e0dfa00d0 100644
--- a/gcc/simplify-rtx.cc
+++ b/gcc/simplify-rtx.cc
@@ -8438,7 +8438,7 @@ test_vector_subregs_fore_back (machine_mode inner_mode)
   rtx x = builder.build ();
 
   test_vector_subregs_modes (x);
-  if (!nunits.is_constant ())
+  if (!nunits.is_constant () && known_ne (nunits, poly_uint16 (1, 1)))
     test_vector_subregs_modes (x, nunits - min_nunits, count);
 }
 
-- 
2.36.1