From 59d6653eba187165903b926321c13a85612e3448 Mon Sep 17 00:00:00 2001
From: Eduard Urbach <admin@akyoto.dev>
Date: Tue, 9 Jul 2024 11:43:33 +0200
Subject: [PATCH] Implemented a basic optimization

---
 src/build/asm/Instructions.go                |  4 +++
 src/build/asm/Optimizer.go                   | 34 ++++++++++++++++++++
 src/build/core/CompileCall.go                |  6 ----
 src/build/core/ExecuteRegisterRegister.go    |  4 +--
 src/build/core/Function.go                   |  7 ++++
 src/build/core/TokenToRegister.go            |  5 +--
 tests/programs/{parameters.q => overwrite.q} |  0
 tests/programs_test.go                       |  2 +-
 8 files changed, 48 insertions(+), 14 deletions(-)
 create mode 100644 src/build/asm/Optimizer.go
 rename tests/programs/{parameters.q => overwrite.q} (100%)

diff --git a/src/build/asm/Instructions.go b/src/build/asm/Instructions.go
index 1adcd9d..57bab73 100644
--- a/src/build/asm/Instructions.go
+++ b/src/build/asm/Instructions.go
@@ -15,6 +15,10 @@ func (a *Assembler) RegisterNumber(mnemonic Mnemonic, reg cpu.Register, number i
 
 // RegisterRegister adds an instruction using two registers.
 func (a *Assembler) RegisterRegister(mnemonic Mnemonic, left cpu.Register, right cpu.Register) {
+	if a.unnecessary(mnemonic, left, right) {
+		return
+	}
+
 	a.Instructions = append(a.Instructions, Instruction{
 		Mnemonic: mnemonic,
 		Data: &RegisterRegister{
diff --git a/src/build/asm/Optimizer.go b/src/build/asm/Optimizer.go
new file mode 100644
index 0000000..d91daa1
--- /dev/null
+++ b/src/build/asm/Optimizer.go
@@ -0,0 +1,34 @@
+package asm
+
+import "git.akyoto.dev/cli/q/src/build/cpu"
+
+// unnecessary returns true if the register/register operation can be skipped.
+func (a *Assembler) unnecessary(mnemonic Mnemonic, left cpu.Register, right cpu.Register) bool {
+	if mnemonic == MOVE && left == right {
+		return true
+	}
+
+	if len(a.Instructions) == 0 {
+		return false
+	}
+
+	last := a.Instructions[len(a.Instructions)-1]
+
+	if mnemonic == MOVE && last.Mnemonic == MOVE {
+		data, isRegReg := last.Data.(*RegisterRegister)
+
+		if !isRegReg {
+			return false
+		}
+
+		if data.Destination == left && data.Source == right {
+			return true
+		}
+
+		if data.Destination == right && data.Source == left {
+			return true
+		}
+	}
+
+	return false
+}
diff --git a/src/build/core/CompileCall.go b/src/build/core/CompileCall.go
index 4f063c9..a70c4b6 100644
--- a/src/build/core/CompileCall.go
+++ b/src/build/core/CompileCall.go
@@ -29,12 +29,6 @@ func (f *Function) CompileCall(root *expression.Expression) error {
 		registers = f.cpu.Syscall[:len(parameters)]
 	}
 
-	for _, register := range f.cpu.Input {
-		if f.cpu.IsUsed(register) {
-			f.SaveRegister(register)
-		}
-	}
-
 	err := f.ExpressionsToRegisters(parameters, registers)
 
 	if err != nil {
diff --git a/src/build/core/ExecuteRegisterRegister.go b/src/build/core/ExecuteRegisterRegister.go
index d10205d..22a6be0 100644
--- a/src/build/core/ExecuteRegisterRegister.go
+++ b/src/build/core/ExecuteRegisterRegister.go
@@ -26,9 +26,7 @@ func (f *Function) ExecuteRegisterRegister(operation token.Token, destination cp
 		f.assembler.RegisterRegister(asm.COMPARE, destination, source)
 
 	case "=":
-		if destination != source {
-			f.assembler.RegisterRegister(asm.MOVE, destination, source)
-		}
+		f.assembler.RegisterRegister(asm.MOVE, destination, source)
 
 	default:
 		return errors.New(&errors.InvalidOperator{Operator: operation.Text()}, f.File, operation.Position)
diff --git a/src/build/core/Function.go b/src/build/core/Function.go
index a9d90b8..4eff587 100644
--- a/src/build/core/Function.go
+++ b/src/build/core/Function.go
@@ -47,6 +47,13 @@ func NewFunction(name string, file *fs.File, body token.List) *Function {
 func (f *Function) Compile() {
 	defer close(f.finished)
 	f.assembler.Label(asm.LABEL, f.Name)
+
+	for _, register := range f.cpu.Input {
+		if f.cpu.IsUsed(register) {
+			f.SaveRegister(register)
+		}
+	}
+
 	f.err = f.CompileTokens(f.Body)
 	f.assembler.Return()
 }
diff --git a/src/build/core/TokenToRegister.go b/src/build/core/TokenToRegister.go
index 7a9c428..3e25685 100644
--- a/src/build/core/TokenToRegister.go
+++ b/src/build/core/TokenToRegister.go
@@ -21,10 +21,7 @@ func (f *Function) TokenToRegister(t token.Token, register cpu.Register) error {
 			return errors.New(&errors.UnknownIdentifier{Name: name}, f.File, t.Position)
 		}
 
-		if register != variable.Register {
-			f.assembler.RegisterRegister(asm.MOVE, register, variable.Register)
-		}
-
+		f.assembler.RegisterRegister(asm.MOVE, register, variable.Register)
 		f.useVariable(variable)
 		return nil
 
diff --git a/tests/programs/parameters.q b/tests/programs/overwrite.q
similarity index 100%
rename from tests/programs/parameters.q
rename to tests/programs/overwrite.q
diff --git a/tests/programs_test.go b/tests/programs_test.go
index c6724ea..3b494c5 100644
--- a/tests/programs_test.go
+++ b/tests/programs_test.go
@@ -21,7 +21,7 @@ var programs = []struct {
 	{"square-sum.q", "", 25},
 	{"chained-calls.q", "", 9},
 	{"nested-calls.q", "", 4},
-	{"parameters.q", "", 3},
+	{"overwrite.q", "", 3},
 	{"reuse.q", "", 3},
 	{"return.q", "", 6},
 	{"reassign.q", "", 2},