[Qemu-devel] [PATCH v3 23/27] tcg-ppc64: Rewrite setcond

[Richard Henderson]

Never use MFCR, as the latency is really high.  Even MFOCRF, at half
the latency of MFCR, isn't as fast as we can do with carry tricks.

The ADDIC+SUBFE trick only works for word-sized operands, as we need
carry-out from bit 63.  So for ppc64 we must extend 32-bit inputs.

Use ISEL if available.

Reviewed-by: Aurelien Jarno <address@hidden>
Signed-off-by: Richard Henderson <address@hidden>
---
 tcg/ppc64/tcg-target.c | 264 +++++++++++++++++++++++++++++++++----------------
 1 file changed, 181 insertions(+), 83 deletions(-)

diff --git a/tcg/ppc64/tcg-target.c b/tcg/ppc64/tcg-target.c
index 96a05d9..30954ff 100644
--- a/tcg/ppc64/tcg-target.c
+++ b/tcg/ppc64/tcg-target.c
@@ -45,6 +45,7 @@ static uint8_t *tb_ret_addr;
 #endif
 
 #define HAVE_ISA_2_06  0
+#define HAVE_ISEL      0
 
 #ifdef CONFIG_USE_GUEST_BASE
 #define TCG_GUEST_BASE_REG 30
@@ -389,6 +390,7 @@ static int tcg_target_const_match (tcg_target_long val,
 #define ORC    XO31(412)
 #define EQV    XO31(284)
 #define NAND   XO31(476)
+#define ISEL   XO31( 15)
 
 #define MULLD  XO31(233)
 #define MULHD  XO31( 73)
@@ -443,6 +445,7 @@ static int tcg_target_const_match (tcg_target_long val,
 #define BT(n, c) (((c)+((n)*4))<<21)
 #define BA(n, c) (((c)+((n)*4))<<16)
 #define BB(n, c) (((c)+((n)*4))<<11)
+#define BC_(n, c) (((c)+((n)*4))<<6)
 
 #define BO_COND_TRUE  BO (12)
 #define BO_COND_FALSE BO ( 4)
@@ -468,6 +471,20 @@ static const uint32_t tcg_to_bc[] = {
     [TCG_COND_GTU] = BC | BI (7, CR_GT) | BO_COND_TRUE,
 };
 
+/* The low bit here is set if the RA and RB fields must be inverted.  */
+static const uint32_t tcg_to_isel[] = {
+    [TCG_COND_EQ]  = ISEL | BC_(7, CR_EQ),
+    [TCG_COND_NE]  = ISEL | BC_(7, CR_EQ) | 1,
+    [TCG_COND_LT]  = ISEL | BC_(7, CR_LT),
+    [TCG_COND_GE]  = ISEL | BC_(7, CR_LT) | 1,
+    [TCG_COND_LE]  = ISEL | BC_(7, CR_GT) | 1,
+    [TCG_COND_GT]  = ISEL | BC_(7, CR_GT),
+    [TCG_COND_LTU] = ISEL | BC_(7, CR_LT),
+    [TCG_COND_GEU] = ISEL | BC_(7, CR_LT) | 1,
+    [TCG_COND_LEU] = ISEL | BC_(7, CR_GT) | 1,
+    [TCG_COND_GTU] = ISEL | BC_(7, CR_GT),
+};
+
 static inline void tcg_out_mov(TCGContext *s, TCGType type,
                                TCGReg ret, TCGReg arg)
 {
@@ -1124,105 +1141,186 @@ static void tcg_out_cmp(TCGContext *s, int cond, 
TCGArg arg1, TCGArg arg2,
     }
 }
 
-static void tcg_out_setcond (TCGContext *s, TCGType type, TCGCond cond,
-                             TCGArg arg0, TCGArg arg1, TCGArg arg2,
-                             int const_arg2)
+static void tcg_out_setcond_eq0(TCGContext *s, TCGType type,
+                                TCGReg dst, TCGReg src)
 {
-    int crop, sh, arg;
+    tcg_out32(s, (type == TCG_TYPE_I64 ? CNTLZD : CNTLZW) | RS(dst) | RA(src));
+    tcg_out_shri64(s, dst, dst, type == TCG_TYPE_I64 ? 6 : 5);
+}
 
-    switch (cond) {
-    case TCG_COND_EQ:
-        if (const_arg2) {
-            if (!arg2) {
-                arg = arg1;
-            }
-            else {
-                arg = 0;
-                if ((uint16_t) arg2 == arg2) {
-                    tcg_out32(s, XORI | SAI(arg1, 0, arg2));
-                }
-                else {
-                    tcg_out_movi (s, type, 0, arg2);
-                    tcg_out32 (s, XOR | SAB (arg1, 0, 0));
-                }
-            }
-        }
-        else {
-            arg = 0;
-            tcg_out32 (s, XOR | SAB (arg1, 0, arg2));
-        }
+static void tcg_out_setcond_ne0(TCGContext *s, TCGReg dst, TCGReg src)
+{
+    /* X != 0 implies X + -1 generates a carry.  Extra addition
+       trickery means: R = X-1 + ~X + C = X-1 + (-X+1) + C = C.  */
+    if (dst != src) {
+        tcg_out32(s, ADDIC | TAI(dst, src, -1));
+        tcg_out32(s, SUBFE | TAB(dst, dst, src));
+    } else {
+        tcg_out32(s, ADDIC | TAI(0, src, -1));
+        tcg_out32(s, SUBFE | TAB(dst, 0, src));
+    }
+}
 
-        if (type == TCG_TYPE_I64) {
-            tcg_out32 (s, CNTLZD | RS (arg) | RA (0));
-            tcg_out_rld (s, RLDICL, arg0, 0, 58, 6);
-        }
-        else {
-            tcg_out32 (s, CNTLZW | RS (arg) | RA (0));
-            tcg_out_rlw(s, RLWINM, arg0, 0, 27, 5, 31);
+static int tcg_gen_setcond_xor(TCGContext *s, TCGReg arg1, TCGArg arg2,
+                               bool const_arg2)
+{
+    if (const_arg2) {
+        if ((uint32_t)arg2 == arg2) {
+            tcg_out_xori32(s, 0, arg1, arg2);
+        } else {
+            tcg_out_movi(s, TCG_TYPE_I64, 0, arg2);
+            tcg_out32(s, XOR | SAB(arg1, 0, 0));
         }
-        break;
+    } else {
+        tcg_out32(s, XOR | SAB(arg1, 0, arg2));
+    }
+    return 0;
+}
 
-    case TCG_COND_NE:
-        if (const_arg2) {
-            if (!arg2) {
-                arg = arg1;
-            }
-            else {
-                arg = 0;
-                if ((uint16_t) arg2 == arg2) {
-                    tcg_out32(s, XORI | SAI(arg1, 0, arg2));
-                } else {
-                    tcg_out_movi (s, type, 0, arg2);
-                    tcg_out32 (s, XOR | SAB (arg1, 0, 0));
-                }
+static void tcg_out_setcond(TCGContext *s, TCGType type, TCGCond cond,
+                            TCGArg arg0, TCGArg arg1, TCGArg arg2,
+                            int const_arg2)
+{
+    bool invert, swap;
+
+    /* Handle common and trivial cases before handling anything else.  */
+    if (arg2 == 0) {
+        switch (cond) {
+        case TCG_COND_EQ:
+            tcg_out_setcond_eq0(s, type, arg0, arg1);
+            return;
+        case TCG_COND_NE:
+            if (type == TCG_TYPE_I32) {
+                tcg_out_ext32u(s, 0, arg1);
+                arg1 = 0;
             }
+            tcg_out_setcond_ne0(s, arg0, arg1);
+            return;
+        case TCG_COND_GE:
+            tcg_out32(s, NOR | SAB(arg1, arg0, arg1));
+            arg1 = arg0;
+            /* FALLTHRU */
+        case TCG_COND_LT:
+            /* Extract the sign bit.  */
+            tcg_out_rld(s, RLDICL, arg0, arg1,
+                        type == TCG_TYPE_I64 ? 1 : 33, 63);
+            return;
+        default:
+            break;
         }
-        else {
-            arg = 0;
-            tcg_out32 (s, XOR | SAB (arg1, 0, arg2));
-        }
+    }
 
-        if (arg == arg1 && arg1 == arg0) {
-            tcg_out32(s, ADDIC | TAI(0, arg, -1));
-            tcg_out32(s, SUBFE | TAB(arg0, 0, arg));
+    /* If we have ISEL, we can implement everything with 3 or 4 insns.
+       All other cases below are also at least 3 insns, so speed up the
+       code generator by not considering them and always using ISEL.  */
+    if (HAVE_ISEL) {
+        int isel, tab;
+
+        tcg_out_cmp(s, cond, arg1, arg2, const_arg2, 7, type);
+
+        isel = tcg_to_isel[cond];
+
+        tcg_out_movi(s, type, arg0, 1);
+        if (isel & 1) {
+            /* arg0 = (bc ? 0 : 1) */
+            tab = TAB(arg0, 0, arg0);
+            isel &= ~1;
+        } else {
+            /* arg0 = (bc ? 1 : 0) */
+            tcg_out_movi(s, type, 0, 0);
+            tab = TAB(arg0, arg0, 0);
         }
-        else {
-            tcg_out32(s, ADDIC | TAI(arg0, arg, -1));
-            tcg_out32(s, SUBFE | TAB(arg0, arg0, arg));
+        tcg_out32(s, isel | tab);
+        return;
+    }
+
+    invert = swap = false;
+    switch (cond) {
+    case TCG_COND_EQ:
+        /* Given that we can ignore the high bits in setcond_eq0, make
+           sure we go through the XORIS+XORI path in setcond_xor.  */
+        if (type == TCG_TYPE_I32) {
+            arg2 = (uint32_t)arg2;
         }
-        break;
+        arg1 = tcg_gen_setcond_xor(s, arg1, arg2, const_arg2);
+        tcg_out_setcond_eq0(s, type, arg0, arg1);
+        return;
 
-    case TCG_COND_GT:
-    case TCG_COND_GTU:
-        sh = 30;
-        crop = 0;
-        goto crtest;
+    case TCG_COND_NE:
+        if (type == TCG_TYPE_I32) {
+            tcg_out32(s, EXTSW | RS(arg1) | RA(0));
+            arg1 = 0;
+            if (const_arg2) {
+                arg2 = (int32_t)arg2;
+            } else {
+                tcg_out32(s, EXTSW | RS(arg2) | RA(arg0));
+                arg2 = arg0;
+            }
+        }
+        arg1 = tcg_gen_setcond_xor(s, arg1, arg2, const_arg2);
+        tcg_out_setcond_ne0(s, arg0, arg1);
+        return;
 
-    case TCG_COND_LT:
+    /* Reduce the ordered relations to GT.  */
     case TCG_COND_LTU:
-        sh = 29;
-        crop = 0;
-        goto crtest;
-
-    case TCG_COND_GE:
-    case TCG_COND_GEU:
-        sh = 31;
-        crop = CRNOR | BT (7, CR_EQ) | BA (7, CR_LT) | BB (7, CR_LT);
-        goto crtest;
-
-    case TCG_COND_LE:
+    case TCG_COND_LT:
+        swap = true;
+        break;
     case TCG_COND_LEU:
-        sh = 31;
-        crop = CRNOR | BT (7, CR_EQ) | BA (7, CR_GT) | BB (7, CR_GT);
-    crtest:
-        tcg_out_cmp(s, cond, arg1, arg2, const_arg2, 7, type);
-        if (crop) tcg_out32 (s, crop);
-        tcg_out32 (s, MFCR | RT (0));
-        tcg_out_rlw(s, RLWINM, arg0, 0, sh, 31, 31);
+    case TCG_COND_LE:
+        invert = true;
+        break;
+    case TCG_COND_GEU:
+    case TCG_COND_GE:
+        swap = true, invert = true;
+        break;
+    case TCG_COND_GTU:
+    case TCG_COND_GT:
         break;
-
     default:
-        tcg_abort ();
+        tcg_abort();
+    }
+
+    /* In 64-bit mode, carry-out is only generated from the 63-rd bit.
+       Thus 32-bit inputs must be sign-extended.  */
+    if (type == TCG_TYPE_I32) {
+        tcg_out32(s, EXTSW | RS(arg1) | RA(0));
+        arg1 = 0;
+        if (const_arg2) {
+            arg2 = (int32_t)arg2;
+        } else {
+            tcg_out32(s, EXTSW | RS(arg2) | RA(arg0));
+            arg2 = arg0;
+        }
+    }
+    if (swap) {
+        if (const_arg2) {
+            tcg_out_movi(s, TCG_TYPE_I64, 0, arg2);
+            arg2 = arg1;
+            arg1 = 0;
+            const_arg2 = false;
+        } else {
+            int t = arg1;
+            arg1 = arg2;
+            arg2 = t;
+        }
+    }
+
+    /* X > Y implies Y - X generates a carry-out.  This works for both
+       signed and unsigned comparisons.  */
+    if (const_arg2 && (int16_t)arg2 == arg2) {
+        tcg_out32(s, SUBFIC | TAI(0, arg1, arg2));
+    } else {
+        if (const_arg2) {
+            tcg_out_movi(s, type, 0, arg2);
+            arg2 = 0;
+        }
+        tcg_out32(s, SUBFC | TAB(0, arg1, arg2));
+    }
+    tcg_out_movi(s, type, arg0, 0);
+    tcg_out32(s, ADDE | TAB(arg0, arg0, arg0));
+    if (invert) {
+        tcg_out32(s, XORI | SAI(arg0, arg0, 1));
     }
 }
 
-- 
1.8.1.4