compiler: move GC passes to the transform package

transform/testdata/gc-stackslots.ll

@@ -0,0 +1,52 @@
+target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-unknown-wasm"
+
+%runtime.stackChainObject = type { %runtime.stackChainObject*, i32 }
+
+@runtime.stackChainStart = external global %runtime.stackChainObject*
+@someGlobal = global i8 3
+
+declare void @runtime.trackPointer(i8* nocapture readonly)
+
+declare noalias nonnull i8* @runtime.alloc(i32)
+
+; Generic function that returns a pointer (that must be tracked).
+define i8* @getPointer() {
+    ret i8* @someGlobal
+}
+
+define i8* @needsStackSlots() {
+  ; Tracked pointer. Although, in this case the value is immediately returned
+  ; so tracking it is not really necessary.
+  %ptr = call i8* @runtime.alloc(i32 4)
+  call void @runtime.trackPointer(i8* %ptr)
+  ret i8* %ptr
+}
+
+; Check some edge cases of pointer tracking.
+define i8* @needsStackSlots2() {
+  ; Only one stack slot should be created for this (but at the moment, one is
+  ; created for each call to runtime.trackPointer).
+  %ptr1 = call i8* @getPointer()
+  call void @runtime.trackPointer(i8* %ptr1)
+  call void @runtime.trackPointer(i8* %ptr1)
+  call void @runtime.trackPointer(i8* %ptr1)
+
+  ; Create a pointer that does not need to be tracked (but is tracked).
+  %ptr2 = getelementptr i8, i8* @someGlobal, i32 0
+  call void @runtime.trackPointer(i8* %ptr2)
+
+  ; Here is finally the point where an allocation happens.
+  %unused = call i8* @runtime.alloc(i32 4)
+  call void @runtime.trackPointer(i8* %unused)
+
+  ret i8* %ptr1
+}
+
+; Return a pointer from a caller. Because it doesn't allocate, no stack objects
+; need to be created.
+define i8* @noAllocatingFunction() {
+  %ptr = call i8* @getPointer()
+  call void @runtime.trackPointer(i8* %ptr)
+  ret i8* %ptr
+}