[Qemu-devel] [PATCH 8/9] tcg-s390: Improve setcond

[Richard Henderson <rth@twiddle.net>]

There are a variety of common cases for which we can use carry tricks to
avoid a conditional branch.  On very new hardware, use LOAD ON CONDITION
instead of a conditional branch.

Signed-off-by: Richard Henderson <rth@twiddle.net>
---
 tcg/s390/tcg-target.c | 97 +++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 91 insertions(+), 6 deletions(-)

diff --git a/tcg/s390/tcg-target.c b/tcg/s390/tcg-target.c
index 54d6dc1..132f71a 100644
--- a/tcg/s390/tcg-target.c
+++ b/tcg/s390/tcg-target.c
@@ -1135,15 +1135,100 @@ static int tgen_cmp(TCGContext *s, TCGType type, TCGCond c, TCGReg r1,
     return tcg_cond_to_s390_cond[c];
 }
 
-static void tgen_setcond(TCGContext *s, TCGType type, TCGCond c,
+static void tgen_setcond(TCGContext *s, TCGType type, TCGCond cond,
                          TCGReg dest, TCGReg c1, TCGArg c2, int c2const)
 {
-    int cc = tgen_cmp(s, type, c, c1, c2, c2const);
+    int cc;
+
+    switch (cond) {
+    case TCG_COND_GTU:
+    case TCG_COND_GT:
+    do_greater:
+        /* The result of a compare has CC=2 for GT and CC=3 unused.
+           ADD LOGICAL WITH CARRY considers (CC & 2) the carry bit.  */
+        tgen_cmp(s, type, cond, c1, c2, c2const);
+        tcg_out_movi(s, type, dest, 0);
+        tcg_out_insn(s, RRE, ALCGR, dest, dest);
+        return;
+
+    case TCG_COND_GEU:
+    do_geu:
+        /* We need "real" carry semantics, so use SUBTRACT LOGICAL
+           instead of COMPARE LOGICAL.  This needs an extra move.  */
+        tcg_out_mov(s, type, TCG_TMP0, c1);
+        if (c2const) {
+            tcg_out_movi(s, TCG_TYPE_I64, dest, 0);
+            if (type == TCG_TYPE_I32) {
+                tcg_out_insn(s, RIL, SLFI, TCG_TMP0, c2);
+            } else {
+                tcg_out_insn(s, RIL, SLGFI, TCG_TMP0, c2);
+            }
+        } else {
+            if (type == TCG_TYPE_I32) {
+                tcg_out_insn(s, RR, SLR, TCG_TMP0, c2);
+            } else {
+                tcg_out_insn(s, RRE, SLGR, TCG_TMP0, c2);
+            }
+            tcg_out_movi(s, TCG_TYPE_I64, dest, 0);
+        }
+        tcg_out_insn(s, RRE, ALCGR, dest, dest);
+        return;
+
+    case TCG_COND_LEU:
+    case TCG_COND_LTU:
+    case TCG_COND_LT:
+        /* Swap operands so that we can use GEU/GTU/GT.  */
+        if (c2const) {
+            tcg_out_movi(s, type, TCG_TMP0, c2);
+            c2 = c1;
+            c2const = 0;
+            c1 = TCG_TMP0;
+        } else {
+            TCGReg t = c1;
+            c1 = c2;
+            c2 = t;
+        }
+        if (cond == TCG_COND_LEU) {
+            goto do_geu;
+        }
+        cond = tcg_swap_cond(cond);
+        goto do_greater;
+
+    case TCG_COND_NE:
+        /* X != 0 is X > 0.  */
+        if (c2const && c2 == 0) {
+            cond = TCG_COND_GTU;
+            goto do_greater;
+        }
+        break;
 
-    /* Emit: r1 = 1; if (cc) goto over; r1 = 0; over:  */
-    tcg_out_movi(s, type, dest, 1);
-    tcg_out_insn(s, RI, BRC, cc, (4 + 4) >> 1);
-    tcg_out_movi(s, type, dest, 0);
+    case TCG_COND_EQ:
+        /* X == 0 is X <= 0 is 0 >= X.  */
+        if (c2const && c2 == 0) {
+            tcg_out_movi(s, TCG_TYPE_I64, TCG_TMP0, 0);
+            c2 = c1;
+            c2const = 0;
+            c1 = TCG_TMP0;
+            goto do_geu;
+        }
+        break;
+
+    default:
+        break;
+    }
+
+    cc = tgen_cmp(s, type, cond, c1, c2, c2const);
+    if (facilities & FACILITY_LOAD_ON_COND) {
+        /* Emit: d = 0, t = 1, d = (cc ? t : d).  */
+        tcg_out_movi(s, TCG_TYPE_I64, dest, 0);
+        tcg_out_movi(s, TCG_TYPE_I64, TCG_TMP0, 1);
+        tcg_out_insn(s, RRF, LOCGR, dest, TCG_TMP0, cc);
+    } else {
+        /* Emit: d = 1; if (cc) goto over; d = 0; over:  */
+        tcg_out_movi(s, type, dest, 1);
+        tcg_out_insn(s, RI, BRC, cc, (4 + 4) >> 1);
+        tcg_out_movi(s, type, dest, 0);
+    }
 }
 
 static void tgen_movcond(TCGContext *s, TCGType type, TCGCond c, TCGReg dest,
-- 
1.9.0