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-rw-r--r--fpu/softfloat-parts.c.inc21
-rw-r--r--include/fpu/softfloat-helpers.h11
-rw-r--r--include/fpu/softfloat-types.h18
-rw-r--r--target/alpha/cpu.c7
-rw-r--r--target/arm/cpu.c1
-rw-r--r--target/hppa/fpu_helper.c11
-rw-r--r--target/i386/tcg/fpu_helper.c8
-rw-r--r--target/mips/fpu_helper.h6
-rw-r--r--target/mips/msa.c9
-rw-r--r--target/ppc/cpu_init.c3
-rw-r--r--target/rx/cpu.c8
-rw-r--r--target/sh4/cpu.c8
-rw-r--r--target/tricore/helper.c1
-rw-r--r--tests/fp/fp-bench.c1
14 files changed, 107 insertions, 6 deletions
diff --git a/fpu/softfloat-parts.c.inc b/fpu/softfloat-parts.c.inc
index 0122b35008..1d09f066c5 100644
--- a/fpu/softfloat-parts.c.inc
+++ b/fpu/softfloat-parts.c.inc
@@ -334,7 +334,8 @@ static void partsN(uncanon_normal)(FloatPartsN *p, float_status *s,
             p->frac_lo &= ~round_mask;
         }
         frac_shr(p, frac_shift);
-    } else if (s->flush_to_zero) {
+    } else if (s->flush_to_zero &&
+               s->ftz_detection == float_ftz_before_rounding) {
         flags |= float_flag_output_denormal_flushed;
         p->cls = float_class_zero;
         exp = 0;
@@ -381,11 +382,19 @@ static void partsN(uncanon_normal)(FloatPartsN *p, float_status *s,
         exp = (p->frac_hi & DECOMPOSED_IMPLICIT_BIT) && !fmt->m68k_denormal;
         frac_shr(p, frac_shift);
 
-        if (is_tiny && (flags & float_flag_inexact)) {
-            flags |= float_flag_underflow;
-        }
-        if (exp == 0 && frac_eqz(p)) {
-            p->cls = float_class_zero;
+        if (is_tiny) {
+            if (s->flush_to_zero) {
+                assert(s->ftz_detection == float_ftz_after_rounding);
+                flags |= float_flag_output_denormal_flushed;
+                p->cls = float_class_zero;
+                exp = 0;
+                frac_clear(p);
+            } else if (flags & float_flag_inexact) {
+                flags |= float_flag_underflow;
+            }
+            if (exp == 0 && frac_eqz(p)) {
+                p->cls = float_class_zero;
+            }
         }
     }
     p->exp = exp;
diff --git a/include/fpu/softfloat-helpers.h b/include/fpu/softfloat-helpers.h
index 4cb30a4822..8983c2748e 100644
--- a/include/fpu/softfloat-helpers.h
+++ b/include/fpu/softfloat-helpers.h
@@ -109,6 +109,12 @@ static inline void set_flush_inputs_to_zero(bool val, float_status *status)
     status->flush_inputs_to_zero = val;
 }
 
+static inline void set_float_ftz_detection(FloatFTZDetection d,
+                                           float_status *status)
+{
+    status->ftz_detection = d;
+}
+
 static inline void set_default_nan_mode(bool val, float_status *status)
 {
     status->default_nan_mode = val;
@@ -183,4 +189,9 @@ static inline bool get_default_nan_mode(const float_status *status)
     return status->default_nan_mode;
 }
 
+static inline FloatFTZDetection get_float_ftz_detection(const float_status *status)
+{
+    return status->ftz_detection;
+}
+
 #endif /* SOFTFLOAT_HELPERS_H */
diff --git a/include/fpu/softfloat-types.h b/include/fpu/softfloat-types.h
index bba1c397bb..53d5eb8521 100644
--- a/include/fpu/softfloat-types.h
+++ b/include/fpu/softfloat-types.h
@@ -305,6 +305,22 @@ typedef enum __attribute__((__packed__)) {
 } FloatInfZeroNaNRule;
 
 /*
+ * When flush_to_zero is set, should we detect denormal results to
+ * be flushed before or after rounding? For most architectures this
+ * should be set to match the tininess_before_rounding setting,
+ * but a few architectures, e.g. MIPS MSA, detect FTZ before
+ * rounding but tininess after rounding.
+ *
+ * This enum is arranged so that the default if the target doesn't
+ * configure it matches the default for tininess_before_rounding
+ * (i.e. "after rounding").
+ */
+typedef enum __attribute__((__packed__)) {
+    float_ftz_after_rounding = 0,
+    float_ftz_before_rounding = 1,
+} FloatFTZDetection;
+
+/*
  * Floating Point Status. Individual architectures may maintain
  * several versions of float_status for different functions. The
  * correct status for the operation is then passed by reference to
@@ -321,6 +337,8 @@ typedef struct float_status {
     bool tininess_before_rounding;
     /* should denormalised results go to zero and set output_denormal_flushed? */
     bool flush_to_zero;
+    /* do we detect and flush denormal results before or after rounding? */
+    FloatFTZDetection ftz_detection;
     /* should denormalised inputs go to zero and set input_denormal_flushed? */
     bool flush_inputs_to_zero;
     bool default_nan_mode;
diff --git a/target/alpha/cpu.c b/target/alpha/cpu.c
index e1b898e575..f5dd744987 100644
--- a/target/alpha/cpu.c
+++ b/target/alpha/cpu.c
@@ -202,6 +202,13 @@ static void alpha_cpu_initfn(Object *obj)
     set_float_2nan_prop_rule(float_2nan_prop_x87, &env->fp_status);
     /* Default NaN: sign bit clear, msb frac bit set */
     set_float_default_nan_pattern(0b01000000, &env->fp_status);
+    /*
+     * TODO: this is incorrect. The Alpha Architecture Handbook version 4
+     * section 4.7.7.11 says that we flush to zero for underflow cases, so
+     * this should be float_ftz_after_rounding to match the
+     * tininess_after_rounding (which is specified in section 4.7.5).
+     */
+    set_float_ftz_detection(float_ftz_before_rounding, &env->fp_status);
 #if defined(CONFIG_USER_ONLY)
     env->flags = ENV_FLAG_PS_USER | ENV_FLAG_FEN;
     cpu_alpha_store_fpcr(env, (uint64_t)(FPCR_INVD | FPCR_DZED | FPCR_OVFD
diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index 32dc7c1e69..8037744300 100644
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -185,6 +185,7 @@ void arm_register_el_change_hook(ARMCPU *cpu, ARMELChangeHookFn *hook,
 static void arm_set_default_fp_behaviours(float_status *s)
 {
     set_float_detect_tininess(float_tininess_before_rounding, s);
+    set_float_ftz_detection(float_ftz_before_rounding, s);
     set_float_2nan_prop_rule(float_2nan_prop_s_ab, s);
     set_float_3nan_prop_rule(float_3nan_prop_s_cab, s);
     set_float_infzeronan_rule(float_infzeronan_dnan_if_qnan, s);
diff --git a/target/hppa/fpu_helper.c b/target/hppa/fpu_helper.c
index 239c027ec5..8ff4b44804 100644
--- a/target/hppa/fpu_helper.c
+++ b/target/hppa/fpu_helper.c
@@ -67,6 +67,17 @@ void HELPER(loaded_fr0)(CPUHPPAState *env)
     set_float_infzeronan_rule(float_infzeronan_dnan_never, &env->fp_status);
     /* Default NaN: sign bit clear, msb-1 frac bit set */
     set_float_default_nan_pattern(0b00100000, &env->fp_status);
+    /*
+     * "PA-RISC 2.0 Architecture" says it is IMPDEF whether the flushing
+     * enabled by FPSR.D happens before or after rounding. We pick "before"
+     * for consistency with tininess detection.
+     */
+    set_float_ftz_detection(float_ftz_before_rounding, &env->fp_status);
+    /*
+     * TODO: "PA-RISC 2.0 Architecture" chapter 10 says that we should
+     * detect tininess before rounding, but we don't set that here so we
+     * get the default tininess after rounding.
+     */
 }
 
 void cpu_hppa_loaded_fr0(CPUHPPAState *env)
diff --git a/target/i386/tcg/fpu_helper.c b/target/i386/tcg/fpu_helper.c
index de6d0b252e..f112c6c673 100644
--- a/target/i386/tcg/fpu_helper.c
+++ b/target/i386/tcg/fpu_helper.c
@@ -188,6 +188,14 @@ void cpu_init_fp_statuses(CPUX86State *env)
     set_float_default_nan_pattern(0b11000000, &env->fp_status);
     set_float_default_nan_pattern(0b11000000, &env->mmx_status);
     set_float_default_nan_pattern(0b11000000, &env->sse_status);
+    /*
+     * TODO: x86 does flush-to-zero detection after rounding (the SDM
+     * section 10.2.3.3 on the FTZ bit of MXCSR says that we flush
+     * when we detect underflow, which x86 does after rounding).
+     */
+    set_float_ftz_detection(float_ftz_before_rounding, &env->fp_status);
+    set_float_ftz_detection(float_ftz_before_rounding, &env->mmx_status);
+    set_float_ftz_detection(float_ftz_before_rounding, &env->sse_status);
 }
 
 static inline uint8_t save_exception_flags(CPUX86State *env)
diff --git a/target/mips/fpu_helper.h b/target/mips/fpu_helper.h
index 6ad1e466cf..08fb409390 100644
--- a/target/mips/fpu_helper.h
+++ b/target/mips/fpu_helper.h
@@ -84,6 +84,12 @@ static inline void fp_reset(CPUMIPSState *env)
      */
     set_float_2nan_prop_rule(float_2nan_prop_s_ab,
                              &env->active_fpu.fp_status);
+    /*
+     * TODO: the spec does't say clearly whether FTZ happens before
+     * or after rounding for normal FPU operations.
+     */
+    set_float_ftz_detection(float_ftz_before_rounding,
+                            &env->active_fpu.fp_status);
 }
 
 /* MSA */
diff --git a/target/mips/msa.c b/target/mips/msa.c
index fc77bfc7b9..32c6acbcc5 100644
--- a/target/mips/msa.c
+++ b/target/mips/msa.c
@@ -48,6 +48,15 @@ void msa_reset(CPUMIPSState *env)
     /* tininess detected after rounding.*/
     set_float_detect_tininess(float_tininess_after_rounding,
                               &env->active_tc.msa_fp_status);
+    /*
+     * MSACSR.FS detects tiny results to flush to zero before rounding
+     * (per "MIPS Architecture for Programmers Volume IV-j: The MIPS64 SIMD
+     * Architecture Module, Revision 1.1" section 3.5.4), even though it
+     * detects tininess after rounding for underflow purposes (section 3.4.2
+     * table 3.3).
+     */
+    set_float_ftz_detection(float_ftz_before_rounding,
+                            &env->active_tc.msa_fp_status);
 
     /*
      * According to MIPS specifications, if one of the two operands is
diff --git a/target/ppc/cpu_init.c b/target/ppc/cpu_init.c
index 8e49051254..062a6e85fb 100644
--- a/target/ppc/cpu_init.c
+++ b/target/ppc/cpu_init.c
@@ -7262,6 +7262,9 @@ static void ppc_cpu_reset_hold(Object *obj, ResetType type)
     /* tininess for underflow is detected before rounding */
     set_float_detect_tininess(float_tininess_before_rounding,
                               &env->fp_status);
+    /* Similarly for flush-to-zero */
+    set_float_ftz_detection(float_ftz_before_rounding, &env->fp_status);
+
     /*
      * PowerPC propagation rules:
      *  1. A if it sNaN or qNaN
diff --git a/target/rx/cpu.c b/target/rx/cpu.c
index 8c50c7a1bc..37a6fdd569 100644
--- a/target/rx/cpu.c
+++ b/target/rx/cpu.c
@@ -103,6 +103,14 @@ static void rx_cpu_reset_hold(Object *obj, ResetType type)
     set_float_2nan_prop_rule(float_2nan_prop_x87, &env->fp_status);
     /* Default NaN value: sign bit clear, set frac msb */
     set_float_default_nan_pattern(0b01000000, &env->fp_status);
+    /*
+     * TODO: "RX Family RXv1 Instruction Set Architecture" is not 100% clear
+     * on whether flush-to-zero should happen before or after rounding, but
+     * section 1.3.2 says that it happens when underflow is detected, and
+     * implies that underflow is detected after rounding. So this may not
+     * be the correct setting.
+     */
+    set_float_ftz_detection(float_ftz_before_rounding, &env->fp_status);
 }
 
 static ObjectClass *rx_cpu_class_by_name(const char *cpu_model)
diff --git a/target/sh4/cpu.c b/target/sh4/cpu.c
index 24a22724c6..4ac693d99b 100644
--- a/target/sh4/cpu.c
+++ b/target/sh4/cpu.c
@@ -130,6 +130,14 @@ static void superh_cpu_reset_hold(Object *obj, ResetType type)
     set_default_nan_mode(1, &env->fp_status);
     /* sign bit clear, set all frac bits other than msb */
     set_float_default_nan_pattern(0b00111111, &env->fp_status);
+    /*
+     * TODO: "SH-4 CPU Core Architecture ADCS 7182230F" doesn't say whether
+     * it detects tininess before or after rounding. Section 6.4 is clear
+     * that flush-to-zero happens when the result underflows, though, so
+     * either this should be "detect ftz after rounding" or else we should
+     * be setting "detect tininess before rounding".
+     */
+    set_float_ftz_detection(float_ftz_before_rounding, &env->fp_status);
 }
 
 static void superh_cpu_disas_set_info(CPUState *cpu, disassemble_info *info)
diff --git a/target/tricore/helper.c b/target/tricore/helper.c
index e8b0ec5161..9898752eb0 100644
--- a/target/tricore/helper.c
+++ b/target/tricore/helper.c
@@ -116,6 +116,7 @@ void fpu_set_state(CPUTriCoreState *env)
     set_flush_inputs_to_zero(1, &env->fp_status);
     set_flush_to_zero(1, &env->fp_status);
     set_float_detect_tininess(float_tininess_before_rounding, &env->fp_status);
+    set_float_ftz_detection(float_ftz_before_rounding, &env->fp_status);
     set_default_nan_mode(1, &env->fp_status);
     /* Default NaN pattern: sign bit clear, frac msb set */
     set_float_default_nan_pattern(0b01000000, &env->fp_status);
diff --git a/tests/fp/fp-bench.c b/tests/fp/fp-bench.c
index eacb39b99c..d90f542ea2 100644
--- a/tests/fp/fp-bench.c
+++ b/tests/fp/fp-bench.c
@@ -496,6 +496,7 @@ static void run_bench(void)
     set_float_3nan_prop_rule(float_3nan_prop_s_cab, &soft_status);
     set_float_infzeronan_rule(float_infzeronan_dnan_if_qnan, &soft_status);
     set_float_default_nan_pattern(0b01000000, &soft_status);
+    set_float_ftz_detection(float_ftz_before_rounding, &soft_status);
 
     f = bench_funcs[operation][precision];
     g_assert(f);