RISC-V: Adjust floating point code gen for LTGT compare

 - Using gcc.dg/torture/pr91323.c as testcase, so no new testcase
   introduced.

 - We use 3 eq compare for LTGT compare before, in order to prevent exception
   flags setting when any input is NaN.

 - According latest GCC document LTGT and discussion on pr91323
   LTGT should signals on NaNs, like GE/GT/LE/LT.

 - So we expand (LTGT a b) to ((LT a b) | (GT a b)) for fit the document.

 - Tested rv64gc/rv32gc bare-metal/linux on qemu and
   rv64gc on HiFive unleashed board with linux.

ChangeLog

gcc/

Kito Cheng  <kito.cheng@sifive.com>

	* config/riscv/riscv.c (riscv_emit_float_compare): Change the code gen
	for LTGT.
	(riscv_rtx_costs): Update cost model for LTGT.

gcc/ChangeLog

+2020-02-24  Kito Cheng  <kito.cheng@sifive.com>
+
+	* config/riscv/riscv.c (riscv_emit_float_compare): Change the code gen
+	for LTGT.
+	(riscv_rtx_costs): Update cost model for LTGT.
+
 2020-02-23  Vladimir Makarov  <vmakarov@redhat.com>
 
 	PR rtl-optimization/93564

gcc/config/riscv/riscv.c

@@ -1703,12 +1703,17 @@ riscv_rtx_costs (rtx x, machine_mode mode, int outer_code, int opno ATTRIBUTE_UN
       return false;
 
     case UNEQ:
-    case LTGT:
       /* (FEQ(A, A) & FEQ(B, B)) compared against FEQ(A, B).  */
       mode = GET_MODE (XEXP (x, 0));
       *total = tune_info->fp_add[mode == DFmode] + COSTS_N_INSNS (3);
       return false;
 
+    case LTGT:
+      /* (FLT(A, A) || FGT(B, B)).  */
+      mode = GET_MODE (XEXP (x, 0));
+      *total = tune_info->fp_add[mode == DFmode] + COSTS_N_INSNS (2);
+      return false;
+
     case UNGE:
     case UNGT:
     case UNLE:
@@ -2239,9 +2244,8 @@ riscv_emit_float_compare (enum rtx_code *code, rtx *op0, rtx *op1)
       break;
 
     case UNEQ:
-    case LTGT:
       /* ordered(a, b) > (a == b) */
-      *code = fp_code == LTGT ? GTU : EQ;
+      *code = EQ;
       tmp0 = riscv_force_binary (word_mode, EQ, cmp_op0, cmp_op0);
       tmp1 = riscv_force_binary (word_mode, EQ, cmp_op1, cmp_op1);
       *op0 = riscv_force_binary (word_mode, AND, tmp0, tmp1);
@@ -2293,6 +2297,13 @@ riscv_emit_float_compare (enum rtx_code *code, rtx *op0, rtx *op1)
       *op1 = const0_rtx;
       break;
 
+    case LTGT:
+      /* (a < b) | (a > b) */
+      *code = IOR;
+      *op0 = riscv_force_binary (word_mode, LT, cmp_op0, cmp_op1);
+      *op1 = riscv_force_binary (word_mode, GT, cmp_op0, cmp_op1);
+      break;
+
     default:
       gcc_unreachable ();
     }