[PATCH v2] RISC-V: Set the natural size of constant vector mask modes to one RVV data vector.

[Li Xu]

If reinterpret vnx2bi as vnx16qi, vnx16qi must occupy no more of the underlying
registers than vnx2bi.

Consider this following case:
void test_vreinterpret_v_b64_i8m1 (uint8_t *in, int8_t *out)
{
  vbool64_t vmask = __riscv_vlm_v_b64 (in, 2);
  vint8m1_t vout = __riscv_vreinterpret_v_b64_i8m1 (vmask);
  __riscv_vse8_v_i8m1(out, vout, 16);
}

compiler parameters: -march=rv64gcv -mabi=lp64d 
--param=riscv-autovec-preference=fixed-vlmax -O3
Compilation fails with:
test_vreinterpret_v_b64_i8m1during RTL pass: expand

test.c: In function 'test_vreinterpret_v_b64_i8m1':
test.c:11:22: internal compiler error: in gen_lowpart_general, at rtlhooks.cc:57
   11 |     vint8m1_t vout = __riscv_vreinterpret_v_b64_i8m1(src);
      |                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
0xf11876 gen_lowpart_general(machine_mode, rtx_def*)
        ../.././riscv-gcc/gcc/rtlhooks.cc:57
0x191435e gen_vreinterpretvnx16qi(rtx_def*, rtx_def*)
        ../.././riscv-gcc/gcc/config/riscv/vector.md:486
0xe08858 maybe_expand_insn(insn_code, unsigned int, expand_operand*)
        ../.././riscv-gcc/gcc/optabs.cc:8213
0x1471209 riscv_vector::function_expander::generate_insn(insn_code)
        ../.././riscv-gcc/gcc/config/riscv/riscv-vector-builtins.cc:3813
0x147629c riscv_vector::function_expander::expand()
        ../.././riscv-gcc/gcc/config/riscv/riscv-vector-builtins.h:520
0x147629c riscv_vector::expand_builtin(unsigned int, tree_node*, rtx_def*)
        ../.././riscv-gcc/gcc/config/riscv/riscv-vector-builtins.cc:4103
0x9868f9 expand_builtin(tree_node*, rtx_def*, rtx_def*, machine_mode, int)
        ../.././riscv-gcc/gcc/builtins.cc:7342

gcc/ChangeLog:

        * config/riscv/riscv.cc (riscv_regmode_natural_size): set the natural 
size of vector mask mode to one rvv register.

gcc/testsuite/ChangeLog:

        * gcc.target/riscv/rvv/autovec/vreinterpet-fixed.c: New test.
---
 gcc/config/riscv/riscv.cc                             |  5 +++++
 .../gcc.target/riscv/rvv/autovec/vreinterpet-fixed.c  | 11 +++++++++++
 2 files changed, 16 insertions(+)
 create mode 100644 
gcc/testsuite/gcc.target/riscv/rvv/autovec/vreinterpet-fixed.c

diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
index 6eb63a9d4de..b9c811bcc43 100644
--- a/gcc/config/riscv/riscv.cc
+++ b/gcc/config/riscv/riscv.cc
@@ -7362,6 +7362,11 @@ riscv_regmode_natural_size (machine_mode mode)
      anything smaller than that.  */
   /* ??? For now, only do this for variable-width RVV registers.
      Doing it for constant-sized registers breaks lower-subreg.c.  */
+
+  /* RVV mask modes always consume a single register.  */
+  if (GET_MODE_CLASS (mode) == MODE_VECTOR_BOOL)
+    return BYTES_PER_RISCV_VECTOR;
+
   if (!riscv_vector_chunks.is_constant () && riscv_v_ext_mode_p (mode))
     {
       if (riscv_v_ext_tuple_mode_p (mode))
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/vreinterpet-fixed.c 
b/gcc/testsuite/gcc.target/riscv/rvv/autovec/vreinterpet-fixed.c
new file mode 100644
index 00000000000..534d5fe0f0a
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/vreinterpet-fixed.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv -mabi=lp64d 
--param=riscv-autovec-preference=fixed-vlmax -O3" } */
+
+#include "riscv_vector.h"
+
+void test_vreinterpret_v_b64_i8m1 (uint8_t *in, int8_t *out)
+{
+  vbool64_t vmask = __riscv_vlm_v_b64 (in, 2);
+  vint8m1_t vout = __riscv_vreinterpret_v_b64_i8m1 (vmask);
+  __riscv_vse8_v_i8m1(out, vout, 16);
+}
-- 
2.17.1