[PATCH] RISC-V: Allow zero operand for DI variants of vssubu.vx

The RISC-V vector machine description relies on the helper function
`sew64_scalar_helper` to emit actual insns for the DI variants of
vssub.vx and vssubu.vx.  This works with vssub.vx, but can cause
problems with vssubu.vx with the scalar operand being constant zero,
because `has_vi_variant_p` returns false, and the operand will be taken
without being loaded into a reg.  The attached testcases can cause an
internal compiler error as a result.

Allowing a constant zero operand in those insns seems to be a simple
solution that only affects minimum existing code.

gcc/ChangeLog:

	* config/riscv/vector.md: Allow zero operand for DI variants of
	vssubu.vx

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/base/vssubu-1.c: New test.
	* gcc.target/riscv/rvv/base/vssubu-2.c: New test.

gcc/config/riscv/vector.md

@@ -4400,10 +4400,10 @@
 	  (sat_int_minus_binop:VI_D
 	    (match_operand:VI_D 3 "register_operand"     " vr, vr, vr, vr")
 	    (vec_duplicate:VI_D
-	      (match_operand:<VEL> 4 "register_operand"  "  r,  r,  r,  r")))
+	      (match_operand:<VEL> 4 "reg_or_0_operand"  "  rJ, rJ, rJ, rJ")))
 	  (match_operand:VI_D 2 "vector_merge_operand"   " vu,  0, vu,  0")))]
   "TARGET_VECTOR"
-  "v<insn>.vx\t%0,%3,%4%p1"
+  "v<insn>.vx\t%0,%3,%z4%p1"
   [(set_attr "type" "<int_binop_insn_type>")
    (set_attr "mode" "<MODE>")])
 
@@ -4422,10 +4422,10 @@
 	    (match_operand:VI_D 3 "register_operand"         " vr, vr, vr, vr")
 	    (vec_duplicate:VI_D
 	      (sign_extend:<VEL>
-	        (match_operand:<VSUBEL> 4 "register_operand" "  r,  r,  r,  r"))))
+		(match_operand:<VSUBEL> 4 "reg_or_0_operand" "  rJ, rJ, rJ, rJ"))))
 	  (match_operand:VI_D 2 "vector_merge_operand"       " vu,  0, vu,  0")))]
   "TARGET_VECTOR && !TARGET_64BIT"
-  "v<insn>.vx\t%0,%3,%4%p1"
+  "v<insn>.vx\t%0,%3,%z4%p1"
   [(set_attr "type" "<int_binop_insn_type>")
    (set_attr "mode" "<MODE>")])
 

gcc/testsuite/gcc.target/riscv/rvv/base/vssubu-1.c

@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -march=rv64gcv -mabi=lp64d" } */
+
+#include <riscv_vector.h>
+
+vuint64m1_t test_vssubu_vx_u64m1(vuint64m1_t op1)
+{
+  return __riscv_vssubu_vx_u64m1(op1,0,0);
+}
+
+/* { dg-final { scan-assembler-not {\tvssubu} } } */

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

@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -march=rv32gcv -mabi=ilp32d" } */
+
+#include <riscv_vector.h>
+
+vuint64m1_t test_vssubu_vx_u64m1(vuint64m1_t op1)
+{
+  return __riscv_vssubu_vx_u64m1(op1,0,0);
+}
+
+/* { dg-final { scan-assembler-not {\tvssubu} } } */