RISC-V: Make VXRM as global register [PR118103]

Inspired by PR118103, the VXRM register should be treated almost the
same as the FRM register, aka cooperatively-managed global register.
Thus, add the VXRM to global_regs to avoid the elimination by the
late-combine pass.

For example as below code:

  21   │
  22   │ void compute ()
  23   │ {
  24   │   size_t vl = __riscv_vsetvl_e16m1 (N);
  25   │   vuint16m1_t va = __riscv_vle16_v_u16m1 (a, vl);
  26   │   vuint16m1_t vb = __riscv_vle16_v_u16m1 (b, vl);
  27   │   vuint16m1_t vc = __riscv_vaaddu_vv_u16m1 (va, vb, __RISCV_VXRM_RDN, vl);
  28   │
  29   │   __riscv_vse16_v_u16m1 (c, vc, vl);
  30   │ }
  31   │
  32   │ int main ()
  33   │ {
  34   │   initialize ();
  35   │   compute();
  36   │
  37   │   return 0;
  38   │ }

After compile with -march=rv64gcv -O3, we will have:

  30   │ compute:
  31   │     csrwi   vxrm,2
  32   │     lui a3,%hi(a)
  33   │     lui a4,%hi(b)
  34   │     addi    a4,a4,%lo(b)
  35   │     vsetivli    zero,4,e16,m1,ta,ma
  36   │     addi    a3,a3,%lo(a)
  37   │     vle16.v v2,0(a4)
  38   │     vle16.v v1,0(a3)
  39   │     lui a4,%hi(c)
  40   │     addi    a4,a4,%lo(c)
  41   │     vaaddu.vv   v1,v1,v2
  42   │     vse16.v v1,0(a4)
  43   │     ret
  44   │     .size   compute, .-compute
  45   │     .section    .text.startup,"ax",@progbits
  46   │     .align  1
  47   │     .globl  main
  48   │     .type   main, @function
  49   │ main:
       |     // csrwi   vxrm,2 deleted after inline
  50   │     addi    sp,sp,-16
  51   │     sd  ra,8(sp)
  52   │     call    initialize
  53   │     lui a3,%hi(a)
  54   │     lui a4,%hi(b)
  55   │     vsetivli    zero,4,e16,m1,ta,ma
  56   │     addi    a4,a4,%lo(b)
  57   │     addi    a3,a3,%lo(a)
  58   │     vle16.v v2,0(a4)
  59   │     vle16.v v1,0(a3)
  60   │     lui a4,%hi(c)
  61   │     addi    a4,a4,%lo(c)
  62   │     li  a0,0
  63   │     vaaddu.vv   v1,v1,v2

The below test suites are passed for this patch.
* The rv64gcv fully regression test.

	PR target/118103

gcc/ChangeLog:

	* config/riscv/riscv.cc (riscv_conditional_register_usage): Add
	the VXRM as the global_regs.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/base/pr118103-2.c: New test.
	* gcc.target/riscv/rvv/base/pr118103-run-2.c: New test.

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

gcc/config/riscv/riscv.cc

@@ -10900,7 +10900,9 @@ riscv_conditional_register_usage (void)
 	call_used_regs[regno] = 1;
     }
 
-  if (!TARGET_VECTOR)
+  if (TARGET_VECTOR)
+    global_regs[VXRM_REGNUM] = 1;
+  else
     {
       for (int regno = V_REG_FIRST; regno <= V_REG_LAST; regno++)
 	fixed_regs[regno] = call_used_regs[regno] = 1;

gcc/testsuite/gcc.target/riscv/rvv/base/pr118103-2.c

@@ -0,0 +1,40 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -march=rv64gcv -mabi=lp64d" } */
+
+#include "riscv_vector.h"
+
+#define N 4
+uint16_t a[N];
+uint16_t b[N];
+uint16_t c[N];
+
+void initialize ()
+{
+  uint16_t tmp_0[N] = { 0xfff, 3213, 238, 275, };
+
+  for (int i = 0; i < N; ++i)
+    a[i] = b[i] = tmp_0[i];
+
+  for (int i = 0; i < N; ++i)
+    c[i] = 0;
+}
+
+void compute ()
+{
+  size_t vl = __riscv_vsetvl_e16m1 (N);
+  vuint16m1_t va = __riscv_vle16_v_u16m1 (a, vl);
+  vuint16m1_t vb = __riscv_vle16_v_u16m1 (b, vl);
+  vuint16m1_t vc = __riscv_vaaddu_vv_u16m1 (va, vb, __RISCV_VXRM_RDN, vl);
+
+  __riscv_vse16_v_u16m1 (c, vc, vl);
+}
+
+int main ()
+{
+  initialize ();
+  compute();
+
+  return 0;
+}
+
+/* { dg-final { scan-assembler-times {csrwi\s+vxrm,\s*[01234]} 2 } } */

gcc/testsuite/gcc.target/riscv/rvv/base/pr118103-run-2.c

@@ -0,0 +1,44 @@
+/* { dg-do run { target { riscv_v } } } */
+/* { dg-options "-O3" } */
+
+#include "riscv_vector.h"
+
+#define N 4
+uint16_t a[N];
+uint16_t b[N];
+uint16_t c[N];
+
+void initialize () {
+  uint16_t tmp_0[N] = { 0xfff, 3213, 238, 275, };
+  uint16_t tmp_1[N] = { 0x2,  823,  39,   9, };
+
+  for (int i = 0; i < N; ++i)
+    {
+      a[i] = tmp_0[i];
+      b[i] = tmp_1[i];
+    }
+
+  for (int i = 0; i < N; ++i)
+    c[i] = 0;
+}
+
+void compute ()
+{
+  size_t vl = __riscv_vsetvl_e16m1 (N);
+  vuint16m1_t va = __riscv_vle16_v_u16m1 (a, vl);
+  vuint16m1_t vb = __riscv_vle16_v_u16m1 (b, vl);
+  vuint16m1_t vc = __riscv_vaaddu_vv_u16m1 (va, vb, __RISCV_VXRM_RDN, vl);
+
+  __riscv_vse16_v_u16m1 (c, vc, vl);
+}
+
+int main ()
+{
+  initialize ();
+  compute ();
+
+  if (c[0] != 2048)
+    __builtin_abort ();
+
+  return 0;
+}