From 9110e83d6d33b8502c541bc56a9a91b601c839dd Mon Sep 17 00:00:00 2001
From: Markku Rossi <mtr@iki.fi>
Date: Wed, 8 May 2024 13:47:51 +0200
Subject: [PATCH] WIP: circuit rewrite patterns.

---
 compiler/circuits/rewrite.go | 52 ++++++++++++++++++++++++++++++++++++
 compiler/ssa/circuitgen.go   |  3 ++-
 2 files changed, 54 insertions(+), 1 deletion(-)
 create mode 100644 compiler/circuits/rewrite.go

diff --git a/compiler/circuits/rewrite.go b/compiler/circuits/rewrite.go
new file mode 100644
index 00000000..b5bebc98
--- /dev/null
+++ b/compiler/circuits/rewrite.go
@@ -0,0 +1,52 @@
+//
+// Copyright (c) 2024 Markku Rossi
+//
+// All rights reserved.
+//
+
+package circuits
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/markkurossi/mpc/circuit"
+)
+
+// Rewrite applies rewrite patterns to the circuit.
+func (cc *Compiler) Rewrite() {
+	var stats circuit.Stats
+
+	start := time.Now()
+
+	for _, g := range cc.Gates {
+		switch g.Op {
+		case circuit.AND:
+			// AND(A,A) = A
+			if g.A == g.B && g.O.NumOutputs() > 0 {
+				stats[g.Op]++
+				g.ShortCircuit(g.A)
+			}
+		case circuit.OR:
+			// OR(A,A) = A
+			if g.A == g.B && g.O.NumOutputs() > 0 {
+				stats[g.Op]++
+				g.ShortCircuit(g.A)
+			}
+		case circuit.XOR:
+			// XOR(A,A) = 0
+			if g.A == g.B && g.O.NumOutputs() > 0 {
+				stats[g.Op]++
+				g.O.SetValue(Zero)
+			}
+		}
+	}
+
+	elapsed := time.Since(start)
+
+	if cc.Params.Diagnostics {
+		fmt.Printf(" - Rewrite:             %12s: %d/%d (%.2f%%)\n",
+			elapsed, stats.Count(), len(cc.Gates),
+			float64(stats.Count())/float64(len(cc.Gates))*100)
+	}
+}
diff --git a/compiler/ssa/circuitgen.go b/compiler/ssa/circuitgen.go
index 200d42f4..ed7dc81c 100644
--- a/compiler/ssa/circuitgen.go
+++ b/compiler/ssa/circuitgen.go
@@ -1,5 +1,5 @@
 //
-// Copyright (c) 2020-2023 Markku Rossi
+// Copyright (c) 2020-2024 Markku Rossi
 //
 // All rights reserved.
 //
@@ -44,6 +44,7 @@ func (prog *Program) CompileCircuit(params *utils.Params) (
 		fmt.Printf("Compiling circuit...\n")
 	}
 	cc.ConstPropagate()
+	cc.Rewrite()
 	cc.ShortCircuitXORZero()
 	if params.OptPruneGates {
 		orig := float64(len(cc.Gates))