From 65a7a1e426ec502df5079c0fb8d7fcd3f4f7fdf4 Mon Sep 17 00:00:00 2001
From: Eduard Urbach <eduard@urbach.dev>
Date: Thu, 27 Aug 2026 19:55:58 +0200
Subject: [PATCH] Removed unused loads during dead code removal

---
 src/ssa/Block.go                            |  7 ++++---
 src/ssa/Load.go                             |  7 ++++---
 tests/dead-value-load.q                     | 21 +++++++++++++++++++++
 tests/{switch-dead-value.q => dead-value.q} |  0
 tests/tests_test.go                         |  3 ++-
 5 files changed, 31 insertions(+), 7 deletions(-)
 create mode 100644 tests/dead-value-load.q
 rename tests/{switch-dead-value.q => dead-value.q} (100%)

diff --git a/src/ssa/Block.go b/src/ssa/Block.go
index f0e03d8..e2f1dac 100644
--- a/src/ssa/Block.go
+++ b/src/ssa/Block.go
@@ -60,10 +60,11 @@ func (b *Block) FindExisting(instr Value) Value {
 			return existing
 		}
 
-		// If we encounter a call, we can't be sure that the value is still the same.
-		// TODO: This is a bit too conservative. We could check if the call affects the value.
+		// If we encounter an instruction with side effects,
+		// we can't be sure that the value is still the same.
+		// TODO: This is a bit too conservative. We could check if the instruction affects the value.
 		switch existing.(type) {
-		case *Call, *CallExtern:
+		case *Call, *CallExtern, *CallPointer, *Store, *Syscall, *Cas:
 			return nil
 		}
 	}
diff --git a/src/ssa/Load.go b/src/ssa/Load.go
index 240ba69..62f77e5 100644
--- a/src/ssa/Load.go
+++ b/src/ssa/Load.go
@@ -24,10 +24,11 @@ func (a *Load) Equals(v Value) bool {
 	return a.Memory == b.Memory
 }
 
-// IsPure returns false because loads read from memory
-// and two equal loads may yield different values.
+// IsPure returns true because loads have no side effects.
+// Dead loads can be removed and two equal loads only deduplicate if
+// nothing between them modifies the memory.
 func (l *Load) IsPure() bool {
-	return false
+	return true
 }
 
 // Inputs returns the memory address of the load.
diff --git a/tests/dead-value-load.q b/tests/dead-value-load.q
new file mode 100644
index 0000000..e8eff98
--- /dev/null
+++ b/tests/dead-value-load.q
@@ -0,0 +1,21 @@
+main() {
+	v := 4
+	a := new(int, 4)
+	a[0] = -39
+	a[1] = 28
+	a[2] = 22
+	a[3] = -31
+	sum := 0
+	sum += a[0]
+	sum += a[1]
+	sum += a[2]
+	sum += a[3]
+	sel := 0
+
+	switch {
+		v > 2 { sel = 7 }
+		_     { sel = -3 }
+	}
+
+	assert sel == 7
+}
\ No newline at end of file
diff --git a/tests/switch-dead-value.q b/tests/dead-value.q
similarity index 100%
rename from tests/switch-dead-value.q
rename to tests/dead-value.q
diff --git a/tests/tests_test.go b/tests/tests_test.go
index 1714954..b17b38c 100644
--- a/tests/tests_test.go
+++ b/tests/tests_test.go
@@ -50,7 +50,6 @@ var tests = []run{
 	{"jump-near", nil, "", "", 0},
 	{"switch", nil, "", "", 0},
 	{"switch-expression", nil, "", "", 0},
-	{"switch-dead-value", nil, "", "", 0},
 	{"phi", nil, "", "", 0},
 	{"phi-simple", nil, "", "", 0},
 	{"phi-advanced", nil, "", "", 0},
@@ -193,6 +192,8 @@ var tests = []run{
 	{"zero-alloc", nil, "", "", 0},
 	{"spill-call", nil, "", "", 0},
 	{"spill-call-binary", nil, "", "", 0},
+	{"dead-value", nil, "", "", 0},
+	{"dead-value-load", nil, "", "", 0},
 }
 
 func TestTests(t *testing.T) {
-- 
2.51.2