target/arm: Correct names of VFP VFNMA and VFNMS insns

In vfp.decode we have the names of the VFNMA and VFNMS instructions
the wrong way around.  The architecture says that bit 6 is the 'op'
bit, which is 1 for VFNMA and 0 for VFNMS, but we label these two
lines of decode the other way around.  This doesn't cause any
user-visible problem because in the handling of these functions in
translate-vfp.c we give VFNMA the behaviour specified for VFNMS and
vice-versa, but it's confusing when reading the code.

Switch the names of the VFP VFNMA and VFNMS instructions in
the decode file and flip the behaviour also.

NB: the instructions VFMA and VFMS *are* decoded with op=0 for
VFMA and op=1 for VFMS; the confusion probably arose because
we assumed VFNMA and VFNMS to be the same way around.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2536
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20240830152156.2046590-1-peter.maydell@linaro.org
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

target/arm/tcg/translate-vfp.c

@@ -2190,8 +2190,8 @@ static bool do_vfm_sp(DisasContext *s, arg_VFMA_sp *a, bool neg_n, bool neg_d)
 static bool do_vfm_dp(DisasContext *s, arg_VFMA_dp *a, bool neg_n, bool neg_d)
 {
     /*
-     * VFNMA : fd = muladd(-fd,  fn, fm)
-     * VFNMS : fd = muladd(-fd, -fn, fm)
+     * VFNMA : fd = muladd(-fd, -fn, fm)
+     * VFNMS : fd = muladd(-fd,  fn, fm)
      * VFMA  : fd = muladd( fd,  fn, fm)
      * VFMS  : fd = muladd( fd, -fn, fm)
      *
@@ -2262,8 +2262,8 @@ static bool do_vfm_dp(DisasContext *s, arg_VFMA_dp *a, bool neg_n, bool neg_d)
 #define MAKE_VFM_TRANS_FNS(PREC) \
     MAKE_ONE_VFM_TRANS_FN(VFMA, PREC, false, false) \
     MAKE_ONE_VFM_TRANS_FN(VFMS, PREC, true, false) \
-    MAKE_ONE_VFM_TRANS_FN(VFNMA, PREC, false, true) \
-    MAKE_ONE_VFM_TRANS_FN(VFNMS, PREC, true, true)
+    MAKE_ONE_VFM_TRANS_FN(VFNMS, PREC, false, true) \
+    MAKE_ONE_VFM_TRANS_FN(VFNMA, PREC, true, true)
 
 MAKE_VFM_TRANS_FNS(hp)
 MAKE_VFM_TRANS_FNS(sp)

target/arm/tcg/vfp.decode

@@ -141,18 +141,18 @@ VDIV_dp      ---- 1110 1.00 .... .... 1011 .0.0 ....        @vfp_dnm_d
 
 VFMA_hp      ---- 1110 1.10 .... .... 1001 .0. 0 ....       @vfp_dnm_s
 VFMS_hp      ---- 1110 1.10 .... .... 1001 .1. 0 ....       @vfp_dnm_s
-VFNMA_hp     ---- 1110 1.01 .... .... 1001 .0. 0 ....       @vfp_dnm_s
-VFNMS_hp     ---- 1110 1.01 .... .... 1001 .1. 0 ....       @vfp_dnm_s
+VFNMS_hp     ---- 1110 1.01 .... .... 1001 .0. 0 ....       @vfp_dnm_s
+VFNMA_hp     ---- 1110 1.01 .... .... 1001 .1. 0 ....       @vfp_dnm_s
 
 VFMA_sp      ---- 1110 1.10 .... .... 1010 .0. 0 ....       @vfp_dnm_s
 VFMS_sp      ---- 1110 1.10 .... .... 1010 .1. 0 ....       @vfp_dnm_s
-VFNMA_sp     ---- 1110 1.01 .... .... 1010 .0. 0 ....       @vfp_dnm_s
-VFNMS_sp     ---- 1110 1.01 .... .... 1010 .1. 0 ....       @vfp_dnm_s
+VFNMS_sp     ---- 1110 1.01 .... .... 1010 .0. 0 ....       @vfp_dnm_s
+VFNMA_sp     ---- 1110 1.01 .... .... 1010 .1. 0 ....       @vfp_dnm_s
 
 VFMA_dp      ---- 1110 1.10 .... .... 1011 .0.0 ....        @vfp_dnm_d
 VFMS_dp      ---- 1110 1.10 .... .... 1011 .1.0 ....        @vfp_dnm_d
-VFNMA_dp     ---- 1110 1.01 .... .... 1011 .0.0 ....        @vfp_dnm_d
-VFNMS_dp     ---- 1110 1.01 .... .... 1011 .1.0 ....        @vfp_dnm_d
+VFNMS_dp     ---- 1110 1.01 .... .... 1011 .0.0 ....        @vfp_dnm_d
+VFNMA_dp     ---- 1110 1.01 .... .... 1011 .1.0 ....        @vfp_dnm_d
 
 VMOV_imm_hp  ---- 1110 1.11 .... .... 1001 0000 .... \
              vd=%vd_sp imm=%vmov_imm