From a083d0806b2d809b57e1e860962f2125bd3f0099 Mon Sep 17 00:00:00 2001
From: Eduard Urbach <eduard@urbach.dev>
Date: Mon, 1 Sep 2025 20:30:13 +0200
Subject: [PATCH] Fixed loop replacements for undefined phi values

---
 src/core/compileLoop.go          |  8 +++++++-
 src/core/errors_test.go          |  1 +
 src/core/testdata/UnusedValue6.q | 13 +++++++++++++
 src/ssa/Copy.go                  |  2 +-
 src/verbose/SSA.go               | 13 +++++++------
 5 files changed, 29 insertions(+), 8 deletions(-)
 create mode 100644 src/core/testdata/UnusedValue6.q

diff --git a/src/core/compileLoop.go b/src/core/compileLoop.go
index f803e15..39f4109 100644
--- a/src/core/compileLoop.go
+++ b/src/core/compileLoop.go
@@ -118,12 +118,18 @@ func (f *Function) compileLoop(loop *ast.Loop) error {
 		block.Loop = loopHead
 
 		for phi := range loopHead.Phis {
+			oldValue := phi.Arguments[0]
+
+			if oldValue == ssa.Undefined {
+				continue
+			}
+
 			for _, instr := range block.Instructions {
 				if instr == phi {
 					continue
 				}
 
-				instr.Replace(phi.Arguments[0], phi)
+				instr.Replace(oldValue, phi)
 			}
 		}
 	}
diff --git a/src/core/errors_test.go b/src/core/errors_test.go
index 710cd95..ef2bc69 100644
--- a/src/core/errors_test.go
+++ b/src/core/errors_test.go
@@ -64,6 +64,7 @@ var errs = []struct {
 	{"UnusedValue3.q", &core.UnusedValue{Value: "\"not used\""}},
 	{"UnusedValue4.q", &core.UnusedValue{Value: "1"}},
 	{"UnusedValue5.q", &core.UnusedValue{Value: "x + 1"}},
+	{"UnusedValue6.q", &core.UnusedValue{Value: "x2"}},
 	{"VariableAlreadyExists.q", &core.VariableAlreadyExists{Name: "x"}},
 	{"VariableAlreadyExists2.q", &core.VariableAlreadyExists{Name: "x"}},
 }
diff --git a/src/core/testdata/UnusedValue6.q b/src/core/testdata/UnusedValue6.q
new file mode 100644
index 0000000..4f8e9b1
--- /dev/null
+++ b/src/core/testdata/UnusedValue6.q
@@ -0,0 +1,13 @@
+main() {
+	x := 0
+	y := 0
+
+	loop {
+		if true {
+			return
+		}
+
+		x2 := x
+		y2 := y
+	}
+}
\ No newline at end of file
diff --git a/src/ssa/Copy.go b/src/ssa/Copy.go
index 0613e13..59f2c07 100644
--- a/src/ssa/Copy.go
+++ b/src/ssa/Copy.go
@@ -31,7 +31,7 @@ func (c *Copy) Inputs() []Value {
 
 // IsConst returns false because a copy is a new value.
 func (c *Copy) IsConst() bool {
-	return false
+	return true
 }
 
 // Replace replaces the value to be copied if it matches.
diff --git a/src/verbose/SSA.go b/src/verbose/SSA.go
index ebd2722..c784764 100644
--- a/src/verbose/SSA.go
+++ b/src/verbose/SSA.go
@@ -23,14 +23,15 @@ func SSA(root *core.Function) {
 			return
 		}
 
-		pointerToIndex := make(map[string]int, len(f.Steps))
+		tmpColor := ansi.Green
+		tmpPrefix := "α"
+		pointerToName := make(map[string]string, len(f.Steps))
+		pointerToName[fmt.Sprintf("%p", ssa.Undefined)] = "?"
 
 		for _, step := range f.Steps {
-			pointerToIndex[fmt.Sprintf("%p", step.Value)] = step.Index
+			pointerToName[fmt.Sprintf("%p", step.Value)] = fmt.Sprintf("%s%d", tmpPrefix, step.Index)
 		}
 
-		tmpColor := ansi.Green
-		tmpPrefix := "α"
 		ansi.Yellow.Println(f.FullName + ":")
 
 		for _, step := range f.Steps {
@@ -73,9 +74,9 @@ func SSA(root *core.Function) {
 						end = len(value) - pos - 2
 					}
 
-					index := pointerToIndex[value[pos:pos+2+end]]
+					name := pointerToName[value[pos:pos+2+end]]
 					fmt.Print(value[:pos])
-					tmpColor.Printf("%s%d", tmpPrefix, index)
+					tmpColor.Printf("%s", name)
 					value = value[pos+2+end:]
 					pos = strings.Index(value, "0x")
 				}
-- 
2.51.2