target/arm: Implement FCVT (scalar, integer) for fp16

Cc: qemu-stable@nongnu.org
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20180512003217.9105-4-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/helper.c

@@ -11427,8 +11427,12 @@ VFP_CONV_FIX_A64(uq, s, 32, 64, uint64)
 #undef VFP_CONV_FIX_A64
 
 /* Conversion to/from f16 can overflow to infinity before/after scaling.
- * Therefore we convert to f64 (which does not round), scale,
+ * Therefore we convert to f64, scale, and then convert f64 to f16; or
- * and then convert f64 to f16 (which may round).
+ * vice versa for conversion to integer.
+ *
+ * For 16- and 32-bit integers, the conversion to f64 never rounds.
+ * For 64-bit integers, any integer that would cause rounding will also
+ * overflow to f16 infinity, so there is no double rounding problem.
  */
 
 static float16 do_postscale_fp16(float64 f, int shift, float_status *fpst)
@@ -11446,6 +11450,16 @@ float16 HELPER(vfp_ultoh)(uint32_t x, uint32_t shift, void *fpst)
     return do_postscale_fp16(uint32_to_float64(x, fpst), shift, fpst);
 }
 
+float16 HELPER(vfp_sqtoh)(uint64_t x, uint32_t shift, void *fpst)
+{
+    return do_postscale_fp16(int64_to_float64(x, fpst), shift, fpst);
+}
+
+float16 HELPER(vfp_uqtoh)(uint64_t x, uint32_t shift, void *fpst)
+{
+    return do_postscale_fp16(uint64_to_float64(x, fpst), shift, fpst);
+}
+
 static float64 do_prescale_fp16(float16 f, int shift, float_status *fpst)
 {
     if (unlikely(float16_is_any_nan(f))) {
@@ -11475,6 +11489,26 @@ uint32_t HELPER(vfp_touhh)(float16 x, uint32_t shift, void *fpst)
     return float64_to_uint16(do_prescale_fp16(x, shift, fpst), fpst);
 }
 
+uint32_t HELPER(vfp_toslh)(float16 x, uint32_t shift, void *fpst)
+{
+    return float64_to_int32(do_prescale_fp16(x, shift, fpst), fpst);
+}
+
+uint32_t HELPER(vfp_toulh)(float16 x, uint32_t shift, void *fpst)
+{
+    return float64_to_uint32(do_prescale_fp16(x, shift, fpst), fpst);
+}
+
+uint64_t HELPER(vfp_tosqh)(float16 x, uint32_t shift, void *fpst)
+{
+    return float64_to_int64(do_prescale_fp16(x, shift, fpst), fpst);
+}
+
+uint64_t HELPER(vfp_touqh)(float16 x, uint32_t shift, void *fpst)
+{
+    return float64_to_uint64(do_prescale_fp16(x, shift, fpst), fpst);
+}
+
 /* Set the current fp rounding mode and return the old one.
  * The argument is a softfloat float_round_ value.
  */

target/arm/helper.h

@@ -151,6 +151,10 @@ DEF_HELPER_3(vfp_touhd_round_to_zero, i64, f64, i32, ptr)
 DEF_HELPER_3(vfp_tould_round_to_zero, i64, f64, i32, ptr)
 DEF_HELPER_3(vfp_touhh, i32, f16, i32, ptr)
 DEF_HELPER_3(vfp_toshh, i32, f16, i32, ptr)
+DEF_HELPER_3(vfp_toulh, i32, f16, i32, ptr)
+DEF_HELPER_3(vfp_toslh, i32, f16, i32, ptr)
+DEF_HELPER_3(vfp_touqh, i64, f16, i32, ptr)
+DEF_HELPER_3(vfp_tosqh, i64, f16, i32, ptr)
 DEF_HELPER_3(vfp_toshs, i32, f32, i32, ptr)
 DEF_HELPER_3(vfp_tosls, i32, f32, i32, ptr)
 DEF_HELPER_3(vfp_tosqs, i64, f32, i32, ptr)
@@ -177,6 +181,8 @@ DEF_HELPER_3(vfp_ultod, f64, i64, i32, ptr)
 DEF_HELPER_3(vfp_uqtod, f64, i64, i32, ptr)
 DEF_HELPER_3(vfp_sltoh, f16, i32, i32, ptr)
 DEF_HELPER_3(vfp_ultoh, f16, i32, i32, ptr)
+DEF_HELPER_3(vfp_sqtoh, f16, i64, i32, ptr)
+DEF_HELPER_3(vfp_uqtoh, f16, i64, i32, ptr)
 
 DEF_HELPER_FLAGS_2(set_rmode, TCG_CALL_NO_RWG, i32, i32, ptr)
 DEF_HELPER_FLAGS_2(set_neon_rmode, TCG_CALL_NO_RWG, i32, i32, env)

target/arm/translate-a64.c

@@ -5511,11 +5511,11 @@ static void handle_fpfpcvt(DisasContext *s, int rd, int rn, int opcode,
                            bool itof, int rmode, int scale, int sf, int type)
 {
     bool is_signed = !(opcode & 1);
-    bool is_double = type;
     TCGv_ptr tcg_fpstatus;
-    TCGv_i32 tcg_shift;
+    TCGv_i32 tcg_shift, tcg_single;
+    TCGv_i64 tcg_double;
 
-    tcg_fpstatus = get_fpstatus_ptr(false);
+    tcg_fpstatus = get_fpstatus_ptr(type == 3);
 
     tcg_shift = tcg_const_i32(64 - scale);
 
@@ -5533,8 +5533,9 @@ static void handle_fpfpcvt(DisasContext *s, int rd, int rn, int opcode,
             tcg_int = tcg_extend;
         }
 
-        if (is_double) {
+        switch (type) {
-            TCGv_i64 tcg_double = tcg_temp_new_i64();
+        case 1: /* float64 */
+            tcg_double = tcg_temp_new_i64();
             if (is_signed) {
                 gen_helper_vfp_sqtod(tcg_double, tcg_int,
                                      tcg_shift, tcg_fpstatus);
@@ -5544,8 +5545,10 @@ static void handle_fpfpcvt(DisasContext *s, int rd, int rn, int opcode,
             }
             write_fp_dreg(s, rd, tcg_double);
             tcg_temp_free_i64(tcg_double);
-        } else {
+            break;
-            TCGv_i32 tcg_single = tcg_temp_new_i32();
+
+        case 0: /* float32 */
+            tcg_single = tcg_temp_new_i32();
             if (is_signed) {
                 gen_helper_vfp_sqtos(tcg_single, tcg_int,
                                      tcg_shift, tcg_fpstatus);
@@ -5555,6 +5558,23 @@ static void handle_fpfpcvt(DisasContext *s, int rd, int rn, int opcode,
             }
             write_fp_sreg(s, rd, tcg_single);
             tcg_temp_free_i32(tcg_single);
+            break;
+
+        case 3: /* float16 */
+            tcg_single = tcg_temp_new_i32();
+            if (is_signed) {
+                gen_helper_vfp_sqtoh(tcg_single, tcg_int,
+                                     tcg_shift, tcg_fpstatus);
+            } else {
+                gen_helper_vfp_uqtoh(tcg_single, tcg_int,
+                                     tcg_shift, tcg_fpstatus);
+            }
+            write_fp_sreg(s, rd, tcg_single);
+            tcg_temp_free_i32(tcg_single);
+            break;
+
+        default:
+            g_assert_not_reached();
         }
     } else {
         TCGv_i64 tcg_int = cpu_reg(s, rd);
@@ -5571,8 +5591,9 @@ static void handle_fpfpcvt(DisasContext *s, int rd, int rn, int opcode,
 
         gen_helper_set_rmode(tcg_rmode, tcg_rmode, tcg_fpstatus);
 
-        if (is_double) {
+        switch (type) {
-            TCGv_i64 tcg_double = read_fp_dreg(s, rn);
+        case 1: /* float64 */
+            tcg_double = read_fp_dreg(s, rn);
             if (is_signed) {
                 if (!sf) {
                     gen_helper_vfp_tosld(tcg_int, tcg_double,
@@ -5590,9 +5611,14 @@ static void handle_fpfpcvt(DisasContext *s, int rd, int rn, int opcode,
                                          tcg_shift, tcg_fpstatus);
                 }
             }
+            if (!sf) {
+                tcg_gen_ext32u_i64(tcg_int, tcg_int);
+            }
             tcg_temp_free_i64(tcg_double);
-        } else {
+            break;
-            TCGv_i32 tcg_single = read_fp_sreg(s, rn);
+
+        case 0: /* float32 */
+            tcg_single = read_fp_sreg(s, rn);
             if (sf) {
                 if (is_signed) {
                     gen_helper_vfp_tosqs(tcg_int, tcg_single,
@@ -5614,14 +5640,39 @@ static void handle_fpfpcvt(DisasContext *s, int rd, int rn, int opcode,
                 tcg_temp_free_i32(tcg_dest);
             }
             tcg_temp_free_i32(tcg_single);
+            break;
+
+        case 3: /* float16 */
+            tcg_single = read_fp_sreg(s, rn);
+            if (sf) {
+                if (is_signed) {
+                    gen_helper_vfp_tosqh(tcg_int, tcg_single,
+                                         tcg_shift, tcg_fpstatus);
+                } else {
+                    gen_helper_vfp_touqh(tcg_int, tcg_single,
+                                         tcg_shift, tcg_fpstatus);
+                }
+            } else {
+                TCGv_i32 tcg_dest = tcg_temp_new_i32();
+                if (is_signed) {
+                    gen_helper_vfp_toslh(tcg_dest, tcg_single,
+                                         tcg_shift, tcg_fpstatus);
+                } else {
+                    gen_helper_vfp_toulh(tcg_dest, tcg_single,
+                                         tcg_shift, tcg_fpstatus);
+                }
+                tcg_gen_extu_i32_i64(tcg_int, tcg_dest);
+                tcg_temp_free_i32(tcg_dest);
+            }
+            tcg_temp_free_i32(tcg_single);
+            break;
+
+        default:
+            g_assert_not_reached();
         }
 
         gen_helper_set_rmode(tcg_rmode, tcg_rmode, tcg_fpstatus);
         tcg_temp_free_i32(tcg_rmode);
-
-        if (!sf) {
-            tcg_gen_ext32u_i64(tcg_int, tcg_int);
-        }
     }
 
     tcg_temp_free_ptr(tcg_fpstatus);
@@ -5791,7 +5842,20 @@ static void disas_fp_int_conv(DisasContext *s, uint32_t insn)
         /* actual FP conversions */
         bool itof = extract32(opcode, 1, 1);
 
-        if (type > 1 || (rmode != 0 && opcode > 1)) {
+        if (rmode != 0 && opcode > 1) {
+            unallocated_encoding(s);
+            return;
+        }
+        switch (type) {
+        case 0: /* float32 */
+        case 1: /* float64 */
+            break;
+        case 3: /* float16 */
+            if (arm_dc_feature(s, ARM_FEATURE_V8_FP16)) {
+                break;
+            }
+            /* fallthru */
+        default:
             unallocated_encoding(s);
             return;
         }