target/arm: Implement v8.1M conditional-select insns

v8.1M brings four new insns to M-profile:
 * CSEL  : Rd = cond ? Rn : Rm
 * CSINC : Rd = cond ? Rn : Rm+1
 * CSINV : Rd = cond ? Rn : ~Rm
 * CSNEG : Rd = cond ? Rn : -Rm

Implement these.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20201019151301.2046-4-peter.maydell@linaro.org

2 files changed, 63 insertions, 0 deletions

diff --git a/target/arm/t32.decode b/target/arm/t32.decode
index 7069d82..d8454bd 100644
--- a/target/arm/t32.decode
+++ b/target/arm/t32.decode
@@ -90,6 +90,9 @@ SBC_rrri         1110101 1011 . .... 0 ... .... .... ....     @s_rrr_shi
 }
 RSB_rrri         1110101 1110 . .... 0 ... .... .... ....     @s_rrr_shi
 
+# v8.1M CSEL and friends
+CSEL             1110101 0010 1 rn:4 10 op:2 rd:4 fcond:4 rm:4
+
 # Data-processing (register-shifted register)
 
 MOV_rxrr         1111 1010 0 shty:2 s:1 rm:4 1111 rd:4 0000 rs:4 \
diff --git a/target/arm/translate.c b/target/arm/translate.c
index d8729e4..9f2201c 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -8262,6 +8262,66 @@ static bool trans_IT(DisasContext *s, arg_IT *a)
     return true;
 }
 
+/* v8.1M CSEL/CSINC/CSNEG/CSINV */
+static bool trans_CSEL(DisasContext *s, arg_CSEL *a)
+{
+    TCGv_i32 rn, rm, zero;
+    DisasCompare c;
+
+    if (!arm_dc_feature(s, ARM_FEATURE_V8_1M)) {
+        return false;
+    }
+
+    if (a->rm == 13) {
+        /* SEE "Related encodings" (MVE shifts) */
+        return false;
+    }
+
+    if (a->rd == 13 || a->rd == 15 || a->rn == 13 || a->fcond >= 14) {
+        /* CONSTRAINED UNPREDICTABLE: we choose to UNDEF */
+        return false;
+    }
+
+    /* In this insn input reg fields of 0b1111 mean "zero", not "PC" */
+    if (a->rn == 15) {
+        rn = tcg_const_i32(0);
+    } else {
+        rn = load_reg(s, a->rn);
+    }
+    if (a->rm == 15) {
+        rm = tcg_const_i32(0);
+    } else {
+        rm = load_reg(s, a->rm);
+    }
+
+    switch (a->op) {
+    case 0: /* CSEL */
+        break;
+    case 1: /* CSINC */
+        tcg_gen_addi_i32(rm, rm, 1);
+        break;
+    case 2: /* CSINV */
+        tcg_gen_not_i32(rm, rm);
+        break;
+    case 3: /* CSNEG */
+        tcg_gen_neg_i32(rm, rm);
+        break;
+    default:
+        g_assert_not_reached();
+    }
+
+    arm_test_cc(&c, a->fcond);
+    zero = tcg_const_i32(0);
+    tcg_gen_movcond_i32(c.cond, rn, c.value, zero, rn, rm);
+    arm_free_cc(&c);
+    tcg_temp_free_i32(zero);
+
+    store_reg(s, a->rd, rn);
+    tcg_temp_free_i32(rm);
+
+    return true;
+}
+
 /*
  * Legacy decoder.
  */