[Qemu-devel] [PATCH v3 6/6] tcg/mips: Support r6 SEL{NE, EQ}Z instead of MOVN/MOVZ

[James Hogan <james.hogan@imgtec.com>]

Extend MIPS movcond implementation to support the SELNEZ/SELEQZ
instructions introduced in MIPS r6 (where MOVN/MOVZ have been removed).

Whereas the "MOVN/MOVZ rd, rs, rt" instructions have the following
semantics:
 rd = [!]rt ? rs : rd

The "SELNEZ/SELEQZ rd, rs, rt" instructions are slightly different:
 rd = [!]rt ? rs : 0

First we ensure that if one of the movcond input values is zero that it
comes last (we can swap the input arguments if we invert the condition).
This is so that it can exactly match one of the SELNEZ/SELEQZ
instructions and avoid the need to emit the other one.

Otherwise we emit the opposite instruction first into a temporary
register, and OR that into the result:
 SELNEZ/SELEQZ  TMP1, v2, c1
 SELEQZ/SELNEZ  ret, v1, c1
 OR             ret, ret, TMP1

Which does the following:
 ret = cond ? v1 : v2

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Aurelien Jarno <aurelien@aurel32.net>
---
Changes in v3:
- Switch to using bool eqz to indicate whether to use SELEQZ / MOVZ
  instead of SELNEZ / MOVN (Richard).
- Add tcg_debug_assert(v2 == ret) for pre-r6 case with comment to remind
  reader that it should be guaranteed via constraints (Richard).

Changes in v2:
- Combine with patch 6 from v1, and drop functional changes to movcond
  implementation pre-r6. We now provide different constraints for
  movcond depending on presence of r6. (thanks Richard for feedback).
---
 tcg/mips/tcg-target.c | 43 +++++++++++++++++++++++++++++++++++++------
 1 file changed, 37 insertions(+), 6 deletions(-)

diff --git a/tcg/mips/tcg-target.c b/tcg/mips/tcg-target.c
index a937b1475d04..eff498991096 100644
--- a/tcg/mips/tcg-target.c
+++ b/tcg/mips/tcg-target.c
@@ -314,6 +314,8 @@ typedef enum {
     OPC_NOR      = OPC_SPECIAL | 0x27,
     OPC_SLT      = OPC_SPECIAL | 0x2A,
     OPC_SLTU     = OPC_SPECIAL | 0x2B,
+    OPC_SELEQZ   = OPC_SPECIAL | 0x35,
+    OPC_SELNEZ   = OPC_SPECIAL | 0x37,
 
     OPC_REGIMM   = 0x01 << 26,
     OPC_BLTZ     = OPC_REGIMM | (0x00 << 16),
@@ -858,13 +860,20 @@ static void tcg_out_brcond2(TCGContext *s, TCGCond cond, TCGReg al, TCGReg ah,
 }
 
 static void tcg_out_movcond(TCGContext *s, TCGCond cond, TCGReg ret,
-                            TCGReg c1, TCGReg c2, TCGReg v)
+                            TCGReg c1, TCGReg c2, TCGReg v1, TCGReg v2)
 {
-    MIPSInsn m_opc = OPC_MOVN;
+    bool eqz = false;
+
+    /* If one of the values is zero, put it last to match SEL*Z instructions */
+    if (use_mips32r6_instructions && v1 == 0) {
+        v1 = v2;
+        v2 = 0;
+        cond = tcg_invert_cond(cond);
+    }
 
     switch (cond) {
     case TCG_COND_EQ:
-        m_opc = OPC_MOVZ;
+        eqz = true;
         /* FALLTHRU */
     case TCG_COND_NE:
         if (c2 != 0) {
@@ -877,14 +886,32 @@ static void tcg_out_movcond(TCGContext *s, TCGCond cond, TCGReg ret,
         /* Minimize code size by preferring a compare not requiring INV.  */
         if (mips_cmp_map[cond] & MIPS_CMP_INV) {
             cond = tcg_invert_cond(cond);
-            m_opc = OPC_MOVZ;
+            eqz = true;
         }
         tcg_out_setcond(s, cond, TCG_TMP0, c1, c2);
         c1 = TCG_TMP0;
         break;
     }
 
-    tcg_out_opc_reg(s, m_opc, ret, v, c1);
+    if (use_mips32r6_instructions) {
+        MIPSInsn m_opc_t = eqz ? OPC_SELEQZ : OPC_SELNEZ;
+        MIPSInsn m_opc_f = eqz ? OPC_SELNEZ : OPC_SELEQZ;
+
+        if (v2 != 0) {
+            tcg_out_opc_reg(s, m_opc_f, TCG_TMP1, v2, c1);
+        }
+        tcg_out_opc_reg(s, m_opc_t, ret, v1, c1);
+        if (v2 != 0) {
+            tcg_out_opc_reg(s, OPC_OR, ret, ret, TCG_TMP1);
+        }
+    } else {
+        MIPSInsn m_opc = eqz ? OPC_MOVZ : OPC_MOVN;
+
+        tcg_out_opc_reg(s, m_opc, ret, v1, c1);
+
+        /* This should be guaranteed via constraints */
+        tcg_debug_assert(v2 == ret);
+    }
 }
 
 static void tcg_out_call_int(TCGContext *s, tcg_insn_unit *arg, bool tail)
@@ -1577,7 +1604,7 @@ static inline void tcg_out_op(TCGContext *s, TCGOpcode opc,
         break;
 
     case INDEX_op_movcond_i32:
-        tcg_out_movcond(s, args[5], a0, a1, a2, args[3]);
+        tcg_out_movcond(s, args[5], a0, a1, a2, args[3], args[4]);
         break;
 
     case INDEX_op_setcond_i32:
@@ -1666,7 +1693,11 @@ static const TCGTargetOpDef mips_op_defs[] = {
     { INDEX_op_deposit_i32, { "r", "0", "rZ" } },
 
     { INDEX_op_brcond_i32, { "rZ", "rZ" } },
+#if !use_mips32r6_instructions
     { INDEX_op_movcond_i32, { "r", "rZ", "rZ", "rZ", "0" } },
+#else
+    { INDEX_op_movcond_i32, { "r", "rZ", "rZ", "rZ", "rZ" } },
+#endif
     { INDEX_op_setcond_i32, { "r", "rZ", "rZ" } },
     { INDEX_op_setcond2_i32, { "r", "rZ", "rZ", "rZ", "rZ" } },
 
-- 
2.4.9