diff --git a/compiler/symbol.go b/compiler/symbol.go
index 6455fb8f..6eec892d 100644
--- a/compiler/symbol.go
+++ b/compiler/symbol.go
@@ -139,6 +139,17 @@ func (c *compilerContext) getFunction(fn *ssa.Function) llvm.Value {
 		for _, attrName := range []string{"noalias", "nonnull"} {
 			llvmFn.AddAttributeAtIndex(0, c.ctx.CreateEnumAttribute(llvm.AttributeKindID(attrName), 0))
 		}
+	case "runtime.sliceAppend":
+		// Appending a slice will only read the to-be-appended slice, it won't
+		// be modified.
+		llvmFn.AddAttributeAtIndex(2, c.ctx.CreateEnumAttribute(llvm.AttributeKindID("nocapture"), 0))
+		llvmFn.AddAttributeAtIndex(2, c.ctx.CreateEnumAttribute(llvm.AttributeKindID("readonly"), 0))
+	case "runtime.sliceCopy":
+		// Copying a slice won't capture any of the parameters.
+		llvmFn.AddAttributeAtIndex(1, c.ctx.CreateEnumAttribute(llvm.AttributeKindID("writeonly"), 0))
+		llvmFn.AddAttributeAtIndex(1, c.ctx.CreateEnumAttribute(llvm.AttributeKindID("nocapture"), 0))
+		llvmFn.AddAttributeAtIndex(2, c.ctx.CreateEnumAttribute(llvm.AttributeKindID("readonly"), 0))
+		llvmFn.AddAttributeAtIndex(2, c.ctx.CreateEnumAttribute(llvm.AttributeKindID("nocapture"), 0))
 	case "runtime.trackPointer":
 		// This function is necessary for tracking pointers on the stack in a
 		// portable way (see gc_stack_portable.go). Indicate to the optimizer
diff --git a/compiler/testdata/slice.ll b/compiler/testdata/slice.ll
index 3502851d..0cc5f8a6 100644
--- a/compiler/testdata/slice.ll
+++ b/compiler/testdata/slice.ll
@@ -60,7 +60,7 @@ entry:
   ret { i32*, i32, i32 } %7
 }
 
-declare { i8*, i32, i32 } @runtime.sliceAppend(i8*, i8*, i32, i32, i32, i32, i8*, i8*)
+declare { i8*, i32, i32 } @runtime.sliceAppend(i8*, i8* nocapture readonly, i32, i32, i32, i32, i8*, i8*)
 
 define hidden { i32*, i32, i32 } @main.sliceAppendSlice(i32* %ints.data, i32 %ints.len, i32 %ints.cap, i32* %added.data, i32 %added.len, i32 %added.cap, i8* %context, i8* %parentHandle) unnamed_addr {
 entry:
@@ -85,4 +85,4 @@ entry:
   ret i32 %copy.n
 }
 
-declare i32 @runtime.sliceCopy(i8*, i8*, i32, i32, i32, i8*, i8*)
+declare i32 @runtime.sliceCopy(i8* nocapture writeonly, i8* nocapture readonly, i32, i32, i32, i8*, i8*)
diff --git a/transform/testdata/allocs2.go b/transform/testdata/allocs2.go
index f01ad167..3e1df07d 100644
--- a/transform/testdata/allocs2.go
+++ b/transform/testdata/allocs2.go
@@ -22,6 +22,13 @@ func main() {
 
 	s4 := make([]byte, 300) // OUT: object allocated on the heap: object size 300 exceeds maximum stack allocation size 256
 	readByteSlice(s4)
+
+	s5 := make([]int, 4) // OUT: object allocated on the heap: escapes at line 27
+	s5 = append(s5, 5)
+
+	s6 := make([]int, 3)
+	s7 := []int{1, 2, 3}
+	copySlice(s6, s7)
 }
 
 func derefInt(x *int) int {
@@ -45,3 +52,7 @@ func returnIntSlice(s []int) []int {
 }
 
 func getUnknownNumber() int
+
+func copySlice(out, in []int) {
+	copy(out, in)
+}