RISC-V: Enable Hoist to GCSE simple constants

Hoist want_to_gcse_p () calls rtx_cost () to compute max distance for
hoist candidates . For a const with cost 1 backend currently returns 0,
causing Hoist to bail and elide GCSE.

Note that constants requiring more than 1 insns to setup were working
already since backend is returning 1 as well. Arguably that needs updating
as well to reflect cost better, but that should be a different change
anyways.

To keep testsuite parity, some V tests need updatinge which started failing
in the new costing regime.

gcc/ChangeLog:
	* gcc/config/riscv.cc (riscv_rtx_costs): Adjust const_int cost.

gcc/testsuite/ChangeLog:
	* gcc.target/riscv/gcse-const.c: New Test
	* gcc.target/riscv/rvv/vsetvl/vlmax_conflict-7.c: Disable for
	  -O2.
	* gcc.target/riscv/rvv/vsetvl/vlmax_conflict-8.c: Ditto.

Signed-off-by: Vineet Gupta <vineetg@rivosinc.com>

gcc/config/riscv/riscv.cc

@@ -2377,14 +2377,9 @@ riscv_rtx_costs (rtx x, machine_mode mode, int outer_code, int opno ATTRIBUTE_UN
     case CONST:
       if ((cost = riscv_const_insns (x)) > 0)
 	{
-	  /* If the constant is likely to be stored in a GPR, SETs of
-	     single-insn constants are as cheap as register sets; we
-	     never want to CSE them.  */
+	  /* Hoist will GCSE constants only if cost is non-zero.  */
 	  if (cost == 1 && outer_code == SET)
-	    *total = 0;
-	  /* When we load a constant more than once, it usually is better
-	     to duplicate the last operation in the sequence than to CSE
-	     the constant itself.  */
+	    *total = COSTS_N_INSNS (1);
 	  else if (outer_code == SET || GET_MODE (x) == VOIDmode)
 	    *total = COSTS_N_INSNS (1);
 	}

gcc/testsuite/gcc.target/riscv/gcse-const.c

@@ -0,0 +1,13 @@
+/* Slightly modified copy of gcc.target/arm/pr40956.c.  */
+/* { dg-options "-Os" }  */
+/* Make sure the constant "6" is loaded into register only once.  */
+/* { dg-final { scan-assembler-times "\tli.*6" 1 } } */
+
+int foo(int p, int* q)
+{
+  if (p!=9)
+    *q = 6;
+  else
+    *(q+1) = 6;
+  return 3;
+}

gcc/testsuite/gcc.target/riscv/rvv/vsetvl/vlmax_conflict-7.c

@@ -21,5 +21,5 @@ void f (int32_t * restrict in, int32_t * restrict out, size_t n, size_t cond, si
 }
 
 /* { dg-final { scan-assembler-times {vsetvli} 4 { target { no-opts "-O0"  no-opts "-O1"  no-opts "-Os" no-opts "-Oz" no-opts "-funroll-loops" no-opts "-g" } } } } */
-/* { dg-final { scan-assembler-times {j\s+\.L[0-9]+\s+\.L[0-9]+:\s+vlm\.v} 1 { target { no-opts "-O0" no-opts "-O1"  no-opts "-Os" no-opts "-Oz" no-opts "-funroll-loops" no-opts "-g" } } } } */
+/* { dg-final { scan-assembler-times {j\s+\.L[0-9]+\s+\.L[0-9]+:\s+vlm\.v} 1 { target { no-opts "-O0" no-opts "-O1" no-opts "-O2" no-opts "-Os" no-opts "-Oz" no-opts "-funroll-loops" no-opts "-g" } } } } */
 /* { dg-final { scan-assembler-times {vsetvli\s+[a-x0-9]+,\s*zero,\s*e8,\s*m8,\s*t[au],\s*m[au]} 3 { target { no-opts "-O0" no-opts "-O1"  no-opts "-Os" no-opts "-Oz" no-opts "-funroll-loops" no-opts "-g" } } } } */

gcc/testsuite/gcc.target/riscv/rvv/vsetvl/vlmax_conflict-8.c

@@ -21,7 +21,7 @@ void f (int32_t * restrict in, int32_t * restrict out, size_t n, size_t cond, si
 }
 
 /* { dg-final { scan-assembler-times {vsetvli} 5 { target { no-opts "-O0"  no-opts "-O1"  no-opts "-Os" no-opts "-Oz" no-opts "-funroll-loops" no-opts "-g" } } } } */
-/* { dg-final { scan-assembler-times {j\s+\.L[0-9]+\s+\.L[0-9]+:\s+vlm\.v} 1 { target { no-opts "-O0" no-opts "-O1"  no-opts "-Os" no-opts "-Oz" no-opts "-funroll-loops" no-opts "-g" } } } } */
+/* { dg-final { scan-assembler-times {j\s+\.L[0-9]+\s+\.L[0-9]+:\s+vlm\.v} 1 { target { no-opts "-O0" no-opts "-O1" no-opts "-O2"  no-opts "-Os" no-opts "-Oz" no-opts "-funroll-loops" no-opts "-g" } } } } */
 /* { dg-final { scan-assembler-times {vsetvli\s+[a-x0-9]+,\s*zero,\s*e8,\s*m8,\s*t[au],\s*m[au]} 3 { target { no-opts "-O0" no-opts "-O1"  no-opts "-Os" no-opts "-Oz" no-opts "-funroll-loops" no-opts "-g" } } } } */
 /* { dg-final { scan-assembler-times {vsetvli\s+[a-x0-9]+,\s*zero,\s*e8,\s*mf8,\s*t[au],\s*m[au]} 1 { target { no-opts "-O0" no-opts "-O1"  no-opts "-Os" no-opts "-Oz" no-opts "-funroll-loops" no-opts "-g" } } } } */
 /* { dg-final { scan-assembler-times {vsetvli\s+[a-x0-9]+,\s*zero,\s*e16,\s*mf2,\s*t[au],\s*m[au]} 1 { target { no-opts "-O0" no-opts "-O1"  no-opts "-Os" no-opts "-Oz" no-opts "-funroll-loops" no-opts "-g" } } } } */