[PULL 30/31] target/i386: Wire up MXCSR.DE and FPUS.DE correctly

[Paolo Bonzini <pbonzini@redhat.com>]

From: Peter Maydell <peter.maydell@linaro.org>

The x86 DE bit in the FPU and MXCSR status is supposed to be set
when an input denormal is consumed. We didn't previously report
this from softfloat, so the x86 code either simply didn't set
the DE bit or else incorrectly wired it up to denormal_flushed,
depending on which register you looked at.

Now we have input_denormal_used we can wire up these DE bits
with the semantics they are supposed to have.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Link: https://lore.kernel.org/r/20250519145114.2786534-4-peter.maydell@linaro.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 target/i386/tcg/fpu_helper.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/target/i386/tcg/fpu_helper.c b/target/i386/tcg/fpu_helper.c
index 4732b718129..b3b23823fda 100644
--- a/target/i386/tcg/fpu_helper.c
+++ b/target/i386/tcg/fpu_helper.c
@@ -215,7 +215,7 @@ static void merge_exception_flags(CPUX86State *env, int old_flags)
                        (new_flags & float_flag_overflow ? FPUS_OE : 0) |
                        (new_flags & float_flag_underflow ? FPUS_UE : 0) |
                        (new_flags & float_flag_inexact ? FPUS_PE : 0) |
-                       (new_flags & float_flag_input_denormal_flushed ? FPUS_DE : 0)));
+                       (new_flags & float_flag_input_denormal_used ? FPUS_DE : 0)));
 }
 
 static inline floatx80 helper_fdiv(CPUX86State *env, floatx80 a, floatx80 b)
@@ -3254,6 +3254,7 @@ void update_mxcsr_status(CPUX86State *env)
 
     /* Set exception flags.  */
     set_float_exception_flags((mxcsr & FPUS_IE ? float_flag_invalid : 0) |
+                              (mxcsr & FPUS_DE ? float_flag_input_denormal_used : 0) |
                               (mxcsr & FPUS_ZE ? float_flag_divbyzero : 0) |
                               (mxcsr & FPUS_OE ? float_flag_overflow : 0) |
                               (mxcsr & FPUS_UE ? float_flag_underflow : 0) |
@@ -3270,14 +3271,8 @@ void update_mxcsr_status(CPUX86State *env)
 void update_mxcsr_from_sse_status(CPUX86State *env)
 {
     int flags = get_float_exception_flags(&env->sse_status);
-    /*
-     * The MXCSR denormal flag has opposite semantics to
-     * float_flag_input_denormal_flushed (the softfloat code sets that flag
-     * only when flushing input denormals to zero, but SSE sets it
-     * only when not flushing them to zero), so is not converted
-     * here.
-     */
     env->mxcsr |= ((flags & float_flag_invalid ? FPUS_IE : 0) |
+                   (flags & float_flag_input_denormal_used ? FPUS_DE : 0) |
                    (flags & float_flag_divbyzero ? FPUS_ZE : 0) |
                    (flags & float_flag_overflow ? FPUS_OE : 0) |
                    (flags & float_flag_underflow ? FPUS_UE : 0) |
-- 
2.49.0