Add experimental peephole optimizer with 5 passes, CLI flags, pragmas, and I/O region protection.

README.md

@@ -201,6 +201,115 @@ c65gm automatically:
 
 **Error Handling:** If ACME is not found, c65gm shows installation instructions and suggests using `compile` mode instead.
 
+## Peephole Optimizer (Experimental)
+
+> **⚠️ Experimental.** This feature is new and actively being developed. All optimizations are **disabled by default** and must be explicitly enabled. While thoroughly tested on real C64 projects, edge cases may exist — always verify your program's behavior when optimization is active.
+
+c65gm includes a peephole optimizer that removes redundant 6502 instructions from the generated assembly. It operates as a post-pass on the compiler output, scanning instruction windows and applying pattern-matching rules where safe.
+
+The optimizer only modifies **generated code** — hand-written `ASM`/`ENDASM` blocks, `SCRIPT` output, and inline assembly are left untouched. It can also be configured to skip memory regions used for I/O (e.g., `$D000-$DFFF` on the C64).
+
+### Optimization Passes
+
+Five passes run in sequence. All are enabled by default when `--opt` is used.
+
+| Pass | Pragma | Name | What it removes |
+|---|---|---|---|
+| 1 | `_P_OPT_STLD` | Store-then-load | `sta X; ...; lda X` → `sta X` when A wasn't modified between |
+| 2 | `_P_OPT_LOAD` | Redundant load | `lda X; ...; lda X` → `lda X` when A already holds X's value |
+| 3 | `_P_OPT_IMM` | Redundant immediate | `lda #N; ...; lda #N` → `lda #N` when A already holds N |
+| 4 | `_P_OPT_JMP` | Jump-to-next | `jmp L; L:` → `L:` when no code between `jmp` and its target |
+| 5 | `_P_OPT_SELF` | Self-assignment | `lda X; sta X` → (removed) when same variable stored back to itself |
+
+### CLI Flags
+
+Available on the `build` and `compile` subcommands:
+
+```
+c65gm build   -i program.c65 --opt [--opt-debug] [--opt-exclude ...] [--opt-exclude-c64-io]
+c65gm compile -i program.c65 --opt [--opt-debug] [--opt-exclude ...] [--opt-exclude-c64-io]
+```
+
+| Flag | Effect |
+|---|---|
+| `--opt` | Enable all 5 optimization passes (equivalent to `#PRAGMA _P_OPT_ALL 1`) |
+| `--opt-debug` | Annotate the assembly output with `[removed]` markers and a summary line showing how many instructions were saved |
+| `--opt-exclude` | Mark an address range as I/O to exclude from store-load optimization. Repeatable. Format: `START:END` with hex (`0x` prefix) or decimal values. |
+| `--opt-exclude-c64-io` | Shorthand for `--opt-exclude 0xD000:0xDFFF`. Convenience for C64 targets. |
+
+### Pragma Equivalents
+
+All CLI flags have equivalent `#PRAGMA` directives in the source code:
+
+```c65
+#PRAGMA _P_OPT_ALL 1           ; enable all passes
+#PRAGMA _P_OPT_LOAD 1          ; enable redundant load pass only
+#PRAGMA _P_OPT_IMM 1           ; enable redundant immediate pass only
+#PRAGMA _P_OPT_JMP 1           ; enable jump-to-next pass only
+#PRAGMA _P_OPT_SELF 1          ; enable self-assignment pass only
+#PRAGMA _P_OPT_STLD 1          ; enable store-then-load pass only
+#PRAGMA _P_OPT_DEBUG 1         ; annotate output with [removed] markers
+#PRAGMA _P_OPT_IO $D000 $DFFF  ; mark C64 I/O range as excluded
+```
+
+Pragmas and CLI flags are **additive** — both can be used together.
+
+### Examples
+
+```bash
+# Enable all passes
+c65gm compile -i game.c65 --opt -o game.asm
+
+# Enable passes with debug annotations (see what was removed)
+c65gm compile -i game.c65 --opt --opt-debug -o game.asm
+
+# Enable passes, protect C64 I/O region (recommended for C64 targets)
+c65gm build -i game.c65 --opt --opt-exclude-c64-io
+
+# Protect custom I/O ranges (e.g., multiple VIC-II register blocks)
+c65gm compile -i game.c65 --opt --opt-exclude 0xD000:0xDFFF --opt-exclude 0xDC00:0xDC0F
+
+# Combined: all passes + debug + I/O protection
+c65gm build -i game.c65 --opt --opt-debug --opt-exclude-c64-io
+
+# Command-line equivalent to #PRAGMA _P_OPT_ALL + #PRAGMA _P_OPT_IO $D000 $DFFF
+c65gm build -i game.c65 --opt --opt-exclude 0xD000:0xDFFF
+```
+
+### Verifying Optimizations
+
+With `--opt-debug`, the assembly output contains:
+
+```
+; --- peephole: 4311 asm lines → 4072 (239 saved) ---
+...
+;     POKE target_addr , value
+; [removed] 	ldy #0
+        lda mem_copy_value
+        sta (mem_copy_target_addr),y
+...
+```
+
+The header shows the instruction count before and after (`X asm lines → Y`), plus the total saved. Each `[removed]` annotation marks an instruction that was eliminated. The annotation is a comment and does not affect assembly.
+
+For a full difference view, compile with and without `--opt` and diff the two `.asm` files:
+
+```bash
+c65gm compile -i game.c65 -o baseline.asm
+c65gm compile -i game.c65 --opt --opt-debug -o optimized.asm
+diff -u baseline.asm optimized.asm | less
+```
+
+### I/O Safety
+
+The optimizer never removes **reads or stores** to addresses marked in the I/O exclusion map. Reading an I/O register (like `$D012` raster line or `$DC01` keyboard matrix) may return different values each time, so redundant load elimination is disabled for those addresses. These can be specified via:
+
+1. **CLI flag**: `--opt-exclude 0xD000:0xDFFF` (repeatable for multiple regions)
+2. **CLI shorthand**: `--opt-exclude-c64-io` for the full C64 I/O page
+3. **Pragma**: `#PRAGMA _P_OPT_IO $D000 $DFFF`
+
+Variable names (like `vic2`, `BORDER_COLOR`) are NOT checked against the I/O map — only literal hex addresses are. For `@`-mapped variables that point to I/O registers, use the `_P_OPT_IO` pragma with their address range.
+
 ### Environment Variables
 - **`C65LIBPATH`**: Search path for `#INCLUDE <file>` directives
   ```bash

internal/compiler/compiler.go

@@ -12,9 +12,12 @@ import (
 
 // Compiler orchestrates the compilation process
 type Compiler struct {
-	ctx         *CompilerContext
+	ctx              *CompilerContext
-	registry    *CommandRegistry
+	registry         *CommandRegistry
-	deferredAsm []string // ASM blocks with _P_ASM_AFTER_VARS pragma
+	deferredAsm      []string            // ASM blocks with _P_ASM_AFTER_VARS pragma
+	CmdlineOpt       bool                // --opt enables all passes
+	CmdlineDebug     bool                // --opt-debug enables debug output
+	CmdlineIORegions []optimizer.IORegion // --opt-exclude ranges
 }
 
 // NewCompiler creates a new compiler with initialized context and registry
@@ -281,12 +284,18 @@ func (c *Compiler) Compile(lines []preproc.Line) ([]string, error) {
 	// Remove unused functions with _P_REMOVE_UNUSED pragma
 	codeOutput, removedFuncs := c.removeUnusedFunctions(codeOutput)
 
+	// Update peephole header to match actual [removed] count after function removal
+	codeOutput = updatePeepholeHeader(codeOutput)
+
 	// Assemble final output with headers and footers
 	return c.assembleOutput(codeOutput, removedFuncs), nil
 }
 
 // isOptimizing returns true if any peephole optimization pragma is active
 func (c *Compiler) isOptimizing() bool {
+	if c.CmdlineOpt {
+		return true
+	}
 	if c.ctx == nil || c.ctx.Pragma == nil {
 		return false
 	}
@@ -314,13 +323,65 @@ func (c *Compiler) getOptimizerConfig() *optimizer.Config {
 	idx := c.ctx.Pragma.GetCurrentPragmaSetIndex()
 	ps := c.ctx.Pragma.GetPragmaSetByIndex(idx)
 	cfg := optimizer.NewConfig(ps)
+
+	// Command-line overrides
+	if c.CmdlineOpt {
+		cfg.EnableLoad = true
+		cfg.EnableImm = true
+		cfg.EnableJmp = true
+		cfg.EnableSelf = true
+		cfg.EnableStoreLoad = true
+	}
+	if c.CmdlineDebug {
+		cfg.Debug = true
+	}
+
 	if !cfg.Any() {
 		return nil
 	}
+
+	// Apply CLI I/O regions before pragma-based ones
+	if len(c.CmdlineIORegions) > 0 {
+		cfg.AddIORegions(c.CmdlineIORegions)
+	}
 	cfg.BuildIOMap(c.ctx.Pragma)
 	return cfg
 }
 
+// updatePeepholeHeader recalculates the peephole header saved count
+// from the actual [removed] annotations present after removeUnusedFunctions.
+func updatePeepholeHeader(codeOutput []string) []string {
+	headerIdx := -1
+	var header string
+	removedCount := 0
+
+	for i, line := range codeOutput {
+		if strings.HasPrefix(line, "; --- peephole:") {
+			headerIdx = i
+			header = line
+		}
+		if strings.HasPrefix(line, "; [removed]") {
+			removedCount++
+		}
+	}
+
+	if headerIdx < 0 {
+		return codeOutput
+	}
+
+	// Extract orig count from the existing header
+	var origCount, oldOptCount int
+	if _, err := fmt.Sscanf(header, "; --- peephole: %d asm lines → %d",
+		&origCount, &oldOptCount); err != nil {
+		return codeOutput
+	}
+
+	newHeader := fmt.Sprintf("; --- peephole: %d asm lines → %d (%d saved) ---",
+		origCount, origCount-removedCount, removedCount)
+	codeOutput[headerIdx] = newHeader
+	return codeOutput
+}
+
 func classString(cls CmdClass) string {
 	switch cls {
 	case CmdLinear:

internal/optimizer/config.go

@@ -1,6 +1,7 @@
 package optimizer
 
 import (
+	"fmt"
 	"strconv"
 	"strings"
 
@@ -70,3 +71,57 @@ func parsePragmaAddr(s string) int {
 	}
 	return int(v)
 }
+
+// IORegion defines an address range to exclude from optimization.
+type IORegion struct {
+	Start, End uint16
+}
+
+// AddIORegions marks all addresses in the given regions as I/O in the IOMap.
+func (c *Config) AddIORegions(regions []IORegion) {
+	for _, r := range regions {
+		for a := r.Start; a <= r.End; a++ {
+			c.IOMap[a] = true
+		}
+	}
+}
+
+// ParseExcludeRange parses a string like "0xD000:0xDFFF" or "53248:57343".
+// Returns an IORegion or an error.
+func ParseExcludeRange(s string) (IORegion, error) {
+	parts := strings.SplitN(s, ":", 2)
+	if len(parts) != 2 {
+		return IORegion{}, fmt.Errorf("expected START:END, got %q", s)
+	}
+
+	start, err := parseExcludeAddr(parts[0])
+	if err != nil {
+		return IORegion{}, fmt.Errorf("invalid start %q: %w", parts[0], err)
+	}
+	end, err := parseExcludeAddr(parts[1])
+	if err != nil {
+		return IORegion{}, fmt.Errorf("invalid end %q: %w", parts[1], err)
+	}
+	if start > end {
+		return IORegion{}, fmt.Errorf("start %s > end %s", parts[0], parts[1])
+	}
+	return IORegion{Start: start, End: end}, nil
+}
+
+func parseExcludeAddr(s string) (uint16, error) {
+	s = strings.TrimSpace(s)
+	// Hex: 0x prefix (case-insensitive)
+	if len(s) > 2 && (s[:2] == "0x" || s[:2] == "0X") {
+		v, err := strconv.ParseUint(s[2:], 16, 16)
+		if err != nil {
+			return 0, err
+		}
+		return uint16(v), nil
+	}
+	// Decimal
+	v, err := strconv.ParseUint(s, 10, 16)
+	if err != nil {
+		return 0, err
+	}
+	return uint16(v), nil
+}

internal/optimizer/config_test.go

@@ -25,6 +25,132 @@ func TestNewConfigWithAll(t *testing.T) {
 	}
 }
 
+func TestParseExcludeRange(t *testing.T) {
+	tests := []struct {
+		name    string
+		input   string
+		wantOk  bool
+		wantS   uint16
+		wantE   uint16
+	}{
+		{"hex", "0xD000:0xDFFF", true, 0xD000, 0xDFFF},
+		{"hex lowercase", "0xd000:0xdfff", true, 0xD000, 0xDFFF},
+		{"hex mixed case", "0XD000:0XdFfF", true, 0xD000, 0xDFFF},
+		{"decimal", "53248:57343", true, 53248, 57343},
+		{"single address", "0xD020:0xD020", true, 0xD020, 0xD020},
+		{"invalid range", "0xFFFF:0x0000", false, 0, 0},
+		{"bad format", "garbage", false, 0, 0},
+		{"bad hex", "0xGGGG:0x0000", false, 0, 0},
+		{"too many colons", "0xD000:0xDFFF:extra", false, 0, 0},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			r, err := ParseExcludeRange(tt.input)
+			if tt.wantOk {
+				if err != nil {
+					t.Errorf("unexpected error: %v", err)
+				}
+				if r.Start != tt.wantS || r.End != tt.wantE {
+					t.Errorf("got %04X:%04X, want %04X:%04X", r.Start, r.End, tt.wantS, tt.wantE)
+				}
+			} else {
+				if err == nil {
+					t.Errorf("expected error, got %04X:%04X", r.Start, r.End)
+				}
+			}
+		})
+	}
+}
+
+func TestAddIORegions(t *testing.T) {
+	cfg := &Config{}
+	cfg.AddIORegions([]IORegion{
+		{Start: 0xD000, End: 0xDFFF},
+	})
+
+	if !cfg.IOMap[0xD000] {
+		t.Error("expected 0xD000 to be marked I/O")
+	}
+	if !cfg.IOMap[0xDFFF] {
+		t.Error("expected 0xDFFF to be marked I/O")
+	}
+	if cfg.IOMap[0xCFFF] {
+		t.Error("expected 0xCFFF to NOT be marked I/O")
+	}
+	if cfg.IOMap[0xE000] {
+		t.Error("expected 0xE000 to NOT be marked I/O")
+	}
+}
+
+func TestAddIORegionsMultiple(t *testing.T) {
+	cfg := &Config{}
+	cfg.AddIORegions([]IORegion{
+		{Start: 0xD000, End: 0xDFFF},
+		{Start: 0xDC00, End: 0xDC0F}, // overlaps — still correct
+	})
+
+	if !cfg.IOMap[0xD000] {
+		t.Error("expected 0xD000 I/O")
+	}
+	if !cfg.IOMap[0xDC00] {
+		t.Error("expected 0xDC00 I/O")
+	}
+	if !cfg.IOMap[0xDC0F] {
+		t.Error("expected 0xDC0F I/O")
+	}
+}
+
+func TestBuildIOMap(t *testing.T) {
+	p := preproc.NewPragma()
+	p.AddPragma("_P_OPT_IO", "$D000 $DFFF")
+
+	// Last pragma set should have _P_OPT_IO
+	ps := p.GetPragmaSetByIndex(p.GetCurrentPragmaSetIndex())
+	cfg := NewConfig(ps)
+	cfg.BuildIOMap(p)
+
+	if !cfg.IOMap[0xD000] {
+		t.Error("expected $D000 I/O from pragma")
+	}
+	if !cfg.IOMap[0xDFFF] {
+		t.Error("expected $DFFF I/O from pragma")
+	}
+}
+
+func TestBuildIOMapMultiple(t *testing.T) {
+	// Simulate two _P_OPT_IO pragmas
+	p := preproc.NewPragma()
+	p.AddPragma("_P_OPT_IO", "$D000 $DFFF")
+	p.AddPragma("_P_OPT_IO", "$DC00 $DC0F")
+	p.AddPragma("_P_SOMETHING_ELSE", "1")
+
+	// BuildIOMap scans ALL sets, finding _P_OPT_IO at index 1 and 2
+	ps := p.GetPragmaSetByIndex(p.GetCurrentPragmaSetIndex())
+	cfg := NewConfig(ps)
+	cfg.BuildIOMap(p)
+
+	if !cfg.IOMap[0xD000] {
+		t.Error("expected $D000 I/O")
+	}
+	if !cfg.IOMap[0xDC00] {
+		t.Error("expected $DC00 I/O")
+	}
+}
+
+func TestBuildIOMapEmpty(t *testing.T) {
+	p := preproc.NewPragma()
+	ps := p.GetPragmaSetByIndex(p.GetCurrentPragmaSetIndex())
+	cfg := NewConfig(ps)
+	cfg.BuildIOMap(p)
+
+	for _, addr := range []uint16{0, 0xD000, 0xFFFF} {
+		if cfg.IOMap[addr] {
+			t.Errorf("address %04X should not be I/O", addr)
+		}
+	}
+}
+
 func TestNewConfigPragmasAccumulate(t *testing.T) {
 	// Pragma sets COPY previous values — so last set has ALL pragmas
 	p := preproc.NewPragma()

internal/optimizer/debug.go

@@ -5,45 +5,46 @@ import "fmt"
 // debugDiff produces annotated output showing original vs optimized code.
 // Lines that were removed are shown with "[removed]" annotation.
 func debugDiff(original, optimized []asmLine) []asmLine {
+	// Count [removed] annotations from the walk, then derive optCount from
+	// origCount - removedCount. This avoids mismatches when later pipeline
+	// steps (e.g. removeUnusedFunctions) remove code that the optimizer saw.
 	origCount := countCodeLines(original)
-	optCount := countCodeLines(optimized)
-	saved := origCount - optCount
 
-	header := fmt.Sprintf("; --- peephole: %d asm lines → %d (%d saved) ---", origCount, optCount, saved)
+	var body []asmLine
-	var result []asmLine
+	oi := 0
-	result = append(result, asmLine{text: header, isComment: true})
+	opi := 0
-
+	removedCount := 0
-	// Walk both arrays in sync. When optimized doesn't have a line
-	// that original has, it was removed.
-	oi := 0 // index into original (pre-stripped)
-	opi := 0 // index into optimized
 
 	for oi < len(original) {
 		origLine := original[oi]
 
 		if opi < len(optimized) && linesMatch(origLine, optimized[opi]) {
-			result = append(result, optimized[opi])
+			body = append(body, optimized[opi])
 			oi++
 			opi++
 		} else if !origLine.isCode {
-			// Non-code line that doesn't match anything — pass through
+			body = append(body, origLine)
-			result = append(result, origLine)
 			oi++
 		} else {
-			// Code line in original but not in optimized → removed
+			body = append(body, asmLine{
-			result = append(result, asmLine{
 				text:      fmt.Sprintf("; [removed] %s", origLine.text),
 				isComment: true,
 			})
+			removedCount++
 			oi++
 		}
 	}
 
-	// Append any remaining optimized lines (shouldn't happen in practice)
 	for ; opi < len(optimized); opi++ {
-		result = append(result, optimized[opi])
+		body = append(body, optimized[opi])
 	}
 
+	optCount := origCount - removedCount
+	header := fmt.Sprintf("; --- peephole: %d asm lines → %d (%d saved) ---",
+		origCount, optCount, removedCount)
+
+	result := []asmLine{{text: header, isComment: true}}
+	result = append(result, body...)
 	return result
 }
 

internal/optimizer/optimizer.go

@@ -15,7 +15,7 @@ func Optimize(lines []string, cfg *Config) []string {
 		parsed = passStoreReload(parsed, cfg)
 	}
 	if cfg.EnableLoad {
-		parsed = passLoadElimination(parsed)
+		parsed = passLoadElimination(parsed, cfg)
 	}
 	if cfg.EnableImm {
 		parsed = passImmElimination(parsed)

internal/optimizer/optimizer_test.go

@@ -47,7 +47,7 @@ func TestPassLoadElimination(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			parsed := parseLines(tt.input)
-			result := passLoadElimination(parsed)
+			result := passLoadElimination(parsed, nil)
 			cleaned := stripOptMarkers(result)
 			if got := len(cleaned); got != tt.expected {
 				t.Errorf("got %d lines, want %d\ninput: %v\noutput: %v", got, tt.expected, tt.input, linesToString(cleaned))
@@ -173,6 +173,38 @@ func TestPassSelfAssignment(t *testing.T) {
 	}
 }
 
+func TestPassLoadIO(t *testing.T) {
+	cfg := &Config{}
+	cfg.IOMap[0xD012] = true // raster line register — changes constantly
+
+	t.Run("IO load not eliminated", func(t *testing.T) {
+		parsed := parseLines(lines("\tlda $D012", "\tlda $D012"))
+		result := passLoadElimination(parsed, cfg)
+		cleaned := stripOptMarkers(result)
+		if len(cleaned) != 2 {
+			t.Errorf("expected 2 lines (IO skip), got %d", len(cleaned))
+		}
+	})
+
+	t.Run("non-IO load eliminated", func(t *testing.T) {
+		parsed := parseLines(lines("\tlda $C000", "\tlda $C000"))
+		result := passLoadElimination(parsed, cfg)
+		cleaned := stripOptMarkers(result)
+		if len(cleaned) != 1 {
+			t.Errorf("expected 1 line (non-IO), got %d", len(cleaned))
+		}
+	})
+
+	t.Run("variable name not caught by IO", func(t *testing.T) {
+		parsed := parseLines(lines("\tlda RASTER_LINE", "\tlda RASTER_LINE"))
+		result := passLoadElimination(parsed, cfg)
+		cleaned := stripOptMarkers(result)
+		if len(cleaned) != 1 {
+			t.Errorf("expected 1 line (var not IO), got %d", len(cleaned))
+		}
+	})
+}
+
 func TestPassLoadNoCommentReset(t *testing.T) {
 	// Comments should NOT reset register state
 	parsed := parseLines(lines(
@@ -181,7 +213,7 @@ func TestPassLoadNoCommentReset(t *testing.T) {
 		"; comment",
 		"\tlda b", // should be redundant
 	))
-	result := passLoadElimination(parsed)
+	result := passLoadElimination(parsed, nil)
 	if len(result) != 3 {
 		t.Errorf("expected 3 lines (comment kept, lda b removed), got %d:\n%v", len(result), linesToString(result))
 	}
@@ -389,13 +421,98 @@ func TestPassStoreReload(t *testing.T) {
 }
 
 func TestPassStoreReloadIO(t *testing.T) {
-	cfg := &Config{}
+	t.Run("c64 border color", func(t *testing.T) {
-	cfg.IOMap[0xD020] = true
+		cfg := &Config{}
+		cfg.IOMap[0xD020] = true
+		parsed := parseLines(lines("\tsta $D020", "\tlda $D020"))
+		result := passStoreReload(parsed, cfg)
+		cleaned := stripOptMarkers(result)
+		if len(cleaned) != 2 {
+			t.Errorf("expected 2 lines (I/O skip), got %d", len(cleaned))
+		}
+	})
 
-	parsed := parseLines(lines("\tsta $D020", "\tlda $D020"))
+	t.Run("non-IO address", func(t *testing.T) {
-	result := passStoreReload(parsed, cfg)
+		cfg := &Config{}
-	cleaned := stripOptMarkers(result)
+		cfg.IOMap[0xD020] = true
-	if len(cleaned) != 2 {
+		parsed := parseLines(lines("\tsta $C000", "\tlda $C000"))
-		t.Errorf("expected 2 lines (I/O skip), got %d", len(cleaned))
+		result := passStoreReload(parsed, cfg)
-	}
+		cleaned := stripOptMarkers(result)
+		if len(cleaned) != 1 {
+			t.Errorf("expected 1 line (non-IO), got %d", len(cleaned))
+		}
+	})
+
+	t.Run("decimal address in IO range", func(t *testing.T) {
+		cfg := &Config{}
+		cfg.IOMap[0xD020] = true
+		// Decimal 53280 = $D020, but IOMap uses hex lookup
+		// The pass checks $ prefix only, decimal addresses won't be caught by IOMap
+		parsed := parseLines(lines("\tsta 53280", "\tlda 53280"))
+		result := passStoreReload(parsed, cfg)
+		cleaned := stripOptMarkers(result)
+		if len(cleaned) != 1 {
+			t.Errorf("expected 1 line (decimal not caught by I/O), got %d", len(cleaned))
+		}
+	})
+
+	t.Run("variable name in IO region", func(t *testing.T) {
+		cfg := &Config{}
+		cfg.IOMap[0xD020] = true
+		// Variable names like VIC_BORDER aren't checked against IOMap
+		parsed := parseLines(lines("\tsta BORDER_COLOR", "\tlda BORDER_COLOR"))
+		result := passStoreReload(parsed, cfg)
+		cleaned := stripOptMarkers(result)
+		if len(cleaned) != 1 {
+			t.Errorf("expected 1 line (var name not I/O), got %d", len(cleaned))
+		}
+	})
+
+	t.Run("decimal address not in IO range", func(t *testing.T) {
+		cfg := &Config{}
+		cfg.IOMap[0xD020] = true
+		parsed := parseLines(lines("\tsta 49152", "\tlda 49152"))
+		result := passStoreReload(parsed, cfg)
+		cleaned := stripOptMarkers(result)
+		if len(cleaned) != 1 {
+			t.Errorf("expected 1 line (decimal not IO), got %d", len(cleaned))
+		}
+	})
+
+	t.Run("IOMap from AddIORegions", func(t *testing.T) {
+		cfg := &Config{}
+		cfg.AddIORegions([]IORegion{{Start: 0xD000, End: 0xDFFF}})
+		parsed := parseLines(lines("\tsta $D020", "\tlda $D020"))
+		result := passStoreReload(parsed, cfg)
+		cleaned := stripOptMarkers(result)
+		if len(cleaned) != 2 {
+			t.Errorf("expected 2 lines (I/O via AddIORegions), got %d", len(cleaned))
+		}
+	})
+
+	t.Run("multiple IO regions", func(t *testing.T) {
+		cfg := &Config{}
+		cfg.AddIORegions([]IORegion{
+			{Start: 0xD000, End: 0xDFFF},
+			{Start: 0xDC00, End: 0xDC0F},
+		})
+		tests := []struct{
+			addr string
+			expect int
+		}{
+			{"$D020", 2},
+			{"$DC00", 2},
+			{"$DC0F", 2},
+			{"$C000", 1},
+			{"$E000", 1},
+		}
+		for _, tt := range tests {
+			parsed := parseLines(lines("\tsta " + tt.addr, "\tlda " + tt.addr))
+			result := passStoreReload(parsed, cfg)
+			cleaned := stripOptMarkers(result)
+			if len(cleaned) != tt.expect {
+				t.Errorf("addr %s: expected %d lines, got %d", tt.addr, tt.expect, len(cleaned))
+			}
+		}
+	})
 }

internal/optimizer/pass_load.go

@@ -5,7 +5,7 @@ import "strings"
 // passLoadElimination removes redundant memory-to-register loads.
 // Pattern: lda X; ... (X not modified) ...; lda X  → remove second
 // Applies to A, X, Y registers identically.
-func passLoadElimination(lines []asmLine) []asmLine {
+func passLoadElimination(lines []asmLine, cfg *Config) []asmLine {
 	rs := newRegState()
 	var result []asmLine
 
@@ -27,7 +27,10 @@ func passLoadElimination(lines []asmLine) []asmLine {
 		// Check for redundant memory load
 		if line.opcode == "lda" && !isImmediate(line.operand) {
 			if isIndexedOperand(line.operand) {
-				// Indexed/indirect addressing: address depends on X/Y, can't track by operand text alone
+				updateRegState(line, rs)
+			} else if isIOAddr(line.operand, cfg) {
+				// I/O register reads may return different values — don't track
+				rs.resetA()
 				updateRegState(line, rs)
 			} else if rs.a.src == line.operand {
 				continue // redundant, remove
@@ -37,6 +40,9 @@ func passLoadElimination(lines []asmLine) []asmLine {
 		} else if line.opcode == "ldx" && !isImmediate(line.operand) {
 			if isIndexedOperand(line.operand) {
 				updateRegState(line, rs)
+			} else if isIOAddr(line.operand, cfg) {
+				rs.resetX()
+				updateRegState(line, rs)
 			} else if rs.x.src == line.operand {
 				continue
 			} else {
@@ -45,6 +51,9 @@ func passLoadElimination(lines []asmLine) []asmLine {
 		} else if line.opcode == "ldy" && !isImmediate(line.operand) {
 			if isIndexedOperand(line.operand) {
 				updateRegState(line, rs)
+			} else if isIOAddr(line.operand, cfg) {
+				rs.resetY()
+				updateRegState(line, rs)
 			} else if rs.y.src == line.operand {
 				continue
 			} else {
@@ -67,6 +76,18 @@ func isIndexedOperand(operand string) bool {
 	return strings.Contains(operand, "(") || strings.Contains(operand, ",")
 }
 
+// isIOAddr returns true if operand is a hex address marked as I/O in the config.
+func isIOAddr(operand string, cfg *Config) bool {
+	if cfg == nil {
+		return false
+	}
+	if !strings.HasPrefix(operand, "$") {
+		return false
+	}
+	addr := parseHexOrDec(operand)
+	return addr >= 0 && addr < 65536 && cfg.IOMap[addr]
+}
+
 func isImmediate(operand string) bool {
 	return len(operand) > 0 && operand[0] == '#'
 }

main.go

@@ -13,6 +13,7 @@ import (
 
 	"c65gm/internal/commands"
 	"c65gm/internal/compiler"
+	"c65gm/internal/optimizer"
 	"c65gm/internal/preproc"
 )
 
@@ -114,20 +115,20 @@ func main() {
 	// Determine mode by output extension
 	if strings.HasSuffix(strings.ToLower(outputFile), ".prg") {
 		// Build mode (compile + assemble)
-		if err := build(inputFile, outputFile, false, false); err != nil {
+		if err := build(inputFile, outputFile, false, false, false, false, false, nil); err != nil {
 			handleError(err)
 		}
 		fmt.Println("Build successful.")
 	} else {
 		// Compile mode (assembly only)
-		if err := compileOnly(inputFile, outputFile); err != nil {
+		if err := compileOnly(inputFile, outputFile, false, false, false, nil); err != nil {
 			handleError(err)
 		}
 		fmt.Println("Compilation successful.")
 	}
 }
 
-func compileOnly(inFile, outFile string) error {
+func compileOnly(inFile, outFile string, opt, optDebug, optC64 bool, optExcludes []string) error {
 	// Preprocess
 	lines, pragma, err := preproc.PreProcess(inFile)
 	if err != nil {
@@ -138,6 +139,20 @@ func compileOnly(inFile, outFile string) error {
 
 	// Create compiler and register commands
 	comp := compiler.NewCompiler(pragma)
+	comp.CmdlineOpt = opt
+	comp.CmdlineDebug = optDebug
+	// Build I/O regions from CLI flags
+	if optC64 {
+		comp.CmdlineIORegions = append(comp.CmdlineIORegions, optimizer.IORegion{Start: 0xD000, End: 0xDFFF})
+	}
+	for _, raw := range optExcludes {
+		region, err := optimizer.ParseExcludeRange(raw)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "Warning: --opt-exclude: %v\n", err)
+			continue
+		}
+		comp.CmdlineIORegions = append(comp.CmdlineIORegions, region)
+	}
 	registerCommands(comp)
 
 	// Compile
@@ -233,36 +248,56 @@ func printUsage() {
 	fmt.Println("  -V, --version Show version")
 }
 
+// excludeFlag is a repeatable flag value for --opt-exclude
+type excludeFlag []string
+
+func (e *excludeFlag) String() string {
+	if len(*e) == 0 {
+		return ""
+	}
+	return strings.Join(*e, ", ")
+}
+
+func (e *excludeFlag) Set(value string) error {
+	*e = append(*e, value)
+	return nil
+}
+
 func runBuildCommand(args []string) {
 	buildCmd := flag.NewFlagSet("build", flag.ExitOnError)
 	input := buildCmd.String("i", "", "input .c65 file (required)")
 	output := buildCmd.String("o", "", "output .prg file (default: <input>.prg)")
 	keepAsm := buildCmd.Bool("keep-asm", false, "keep intermediate assembly file")
 	noCBM := buildCmd.Bool("no-cbm", false, "don't add -f cbm flag to ACME")
-	
+	opt := buildCmd.Bool("opt", false, "enable all optimizations")
+	optDebug := buildCmd.Bool("opt-debug", false, "show optimization changes in output")
+	optC64 := buildCmd.Bool("opt-exclude-c64-io", false, "exclude C64 I/O region ($D000-$DFFF) from optimization")
+	var optExcludes excludeFlag
+	buildCmd.Var(&optExcludes, "opt-exclude", "exclude address range from optimization (repeatable, format: START:END)")
+
 	if err := buildCmd.Parse(args); err != nil {
 		fmt.Fprintf(os.Stderr, "Error parsing flags: %v\n", err)
 		os.Exit(1)
 	}
-	
+
 	if *input == "" {
 		fmt.Fprintln(os.Stderr, "Error: -i flag is required")
 		buildCmd.Usage()
 		os.Exit(1)
 	}
-	
+
 	// Default output filename
 	if *output == "" {
 		base := strings.TrimSuffix(filepath.Base(*input), filepath.Ext(*input))
 		*output = base + ".prg"
 	}
-	
+
 	// Ensure output has .prg extension
 	if !strings.HasSuffix(strings.ToLower(*output), ".prg") {
 		*output = *output + ".prg"
 	}
-	
+
-	if err := build(*input, *output, *keepAsm, *noCBM); err != nil {
+	if err := build(*input, *output, *keepAsm, *noCBM, *opt, *optDebug, *optC64, []string(optExcludes)); err != nil {
 		handleError(err)
 	}
 	fmt.Println("Build successful.")
@@ -272,36 +307,41 @@ func runCompileCommand(args []string) {
 	compileCmd := flag.NewFlagSet("compile", flag.ExitOnError)
 	input := compileCmd.String("i", "", "input .c65 file (required)")
 	output := compileCmd.String("o", "", "output .asm file (default: <input>.asm)")
-	
+	opt := compileCmd.Bool("opt", false, "enable all optimizations")
+	optDebug := compileCmd.Bool("opt-debug", false, "show optimization changes in output")
+	optC64 := compileCmd.Bool("opt-exclude-c64-io", false, "exclude C64 I/O region ($D000-$DFFF) from optimization")
+	var optExcludes excludeFlag
+	compileCmd.Var(&optExcludes, "opt-exclude", "exclude address range from optimization (repeatable, format: START:END)")
+
 	if err := compileCmd.Parse(args); err != nil {
 		fmt.Fprintf(os.Stderr, "Error parsing flags: %v\n", err)
 		os.Exit(1)
 	}
-	
+
 	if *input == "" {
 		fmt.Fprintln(os.Stderr, "Error: -i flag is required")
 		compileCmd.Usage()
 		os.Exit(1)
 	}
-	
+
 	// Default output filename
 	if *output == "" {
 		base := strings.TrimSuffix(filepath.Base(*input), filepath.Ext(*input))
 		*output = base + ".asm"
 	}
-	
+
 	// Ensure output has .asm extension
 	if !strings.HasSuffix(strings.ToLower(*output), ".asm") {
 		*output = *output + ".asm"
 	}
-	
+
-	if err := compileOnly(*input, *output); err != nil {
+	if err := compileOnly(*input, *output, *opt, *optDebug, *optC64, []string(optExcludes)); err != nil {
 		handleError(err)
 	}
 	fmt.Println("Compilation successful.")
 }
 
-func build(inputFile, outputFile string, keepAsm, noCBM bool) error {
+func build(inputFile, outputFile string, keepAsm, noCBM, opt, optDebug, optC64 bool, optExcludes []string) error {
 	// Check if ACME is available before starting compilation
 	if err := checkACMEAvailable(); err != nil {
 		return err
@@ -312,7 +352,7 @@ func build(inputFile, outputFile string, keepAsm, noCBM bool) error {
 	asmFile := base + ".asm"
 	
 	// Compile to assembly
-	if err := compileOnly(inputFile, asmFile); err != nil {
+	if err := compileOnly(inputFile, asmFile, opt, optDebug, optC64, optExcludes); err != nil {
 		return fmt.Errorf("compilation failed: %w", err)
 	}