[PULL,08/68] target/arm: Adjust exception flag handling for AH = 1

Commit Message

Peter Maydell Feb. 11, 2025, 4:24 p.m. UTC

When FPCR.AH = 1, some of the cumulative exception flags in the FPSR
behave slightly differently for A64 operations:
 * IDC is set when a denormal input is used without flushing
 * IXC (Inexact) is set when an output denormal is flushed to zero

Update vfp_get_fpsr_from_host() to do this.

Note that because half-precision operations never set IDC, we now
need to add float_flag_input_denormal_used to the set we mask out of
fp_status_f16_a64.

Signed-off-by: Peter Maydell <[e-mail]>
Reviewed-by: Richard Henderson <[e-mail]>
---
 target/arm/vfp_helper.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

Patch

diff --git a/target/arm/vfp_helper.c b/target/arm/vfp_helper.c
index ef85c186f17..62b86d56b8e 100644
--- a/target/arm/vfp_helper.c
+++ b/target/arm/vfp_helper.c
@@ -78,7 +78,7 @@  static void arm_set_ah_fp_behaviours(float_status *s)
 #ifdef CONFIG_TCG
 
 /* Convert host exception flags to vfp form.  */
-static inline uint32_t vfp_exceptbits_from_host(int host_bits)
+static inline uint32_t vfp_exceptbits_from_host(int host_bits, bool ah)
 {
     uint32_t target_bits = 0;
 
@@ -100,6 +100,16 @@  static inline uint32_t vfp_exceptbits_from_host(int host_bits)
     if (host_bits & float_flag_input_denormal_flushed) {
         target_bits |= FPSR_IDC;
     }
+    /*
+     * With FPCR.AH, IDC is set when an input denormal is used,
+     * and flushing an output denormal to zero sets both IXC and UFC.
+     */
+    if (ah && (host_bits & float_flag_input_denormal_used)) {
+        target_bits |= FPSR_IDC;
+    }
+    if (ah && (host_bits & float_flag_output_denormal_flushed)) {
+        target_bits |= FPSR_IXC;
+    }
     return target_bits;
 }
 
@@ -117,7 +127,7 @@  static uint32_t vfp_get_fpsr_from_host(CPUARMState *env)
 
     a64_flags |= get_float_exception_flags(&env->vfp.fp_status_a64);
     a64_flags |= (get_float_exception_flags(&env->vfp.fp_status_f16_a64)
-          & ~float_flag_input_denormal_flushed);
+          & ~(float_flag_input_denormal_flushed | float_flag_input_denormal_used));
     /*
      * Flushing an input denormal *only* because FPCR.FIZ == 1 does
      * not set FPSR.IDC; if FPCR.FZ is also set then this takes
@@ -129,7 +139,8 @@  static uint32_t vfp_get_fpsr_from_host(CPUARMState *env)
     if ((env->vfp.fpcr & (FPCR_FZ | FPCR_AH)) != FPCR_FZ) {
         a64_flags &= ~float_flag_input_denormal_flushed;
     }
-    return vfp_exceptbits_from_host(a32_flags | a64_flags);
+    return vfp_exceptbits_from_host(a64_flags, env->vfp.fpcr & FPCR_AH) |
+        vfp_exceptbits_from_host(a32_flags, false);
 }
 
 static void vfp_clear_float_status_exc_flags(CPUARMState *env)