compiler: move NonConstGlobals pass to transform package

transform/globals.go

@@ -18,3 +18,16 @@ func ApplyFunctionSections(mod llvm.Module) {
 		llvmFn = llvm.NextFunction(llvmFn)
 	}
 }
+
+// NonConstGlobals turns all global constants into global variables. This works
+// around a limitation on Harvard architectures (e.g. AVR), where constant and
+// non-constant pointers point to a different address space. Normal pointer
+// behavior is restored by using the data space only, at the cost of RAM for
+// constant global variables.
+func NonConstGlobals(mod llvm.Module) {
+	global := mod.FirstGlobal()
+	for !global.IsNil() {
+		global.SetGlobalConstant(false)
+		global = llvm.NextGlobal(global)
+	}
+}

transform/globals_test.go

@@ -12,3 +12,10 @@ func TestApplyFunctionSections(t *testing.T) {
 		ApplyFunctionSections(mod)
 	})
 }
+
+func TestNonConstGlobals(t *testing.T) {
+	t.Parallel()
+	testTransform(t, "testdata/globals-non-const", func(mod llvm.Module) {
+		NonConstGlobals(mod)
+	})
+}

transform/testdata/globals-non-const.ll

@@ -0,0 +1,5 @@
+target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "armv7em-none-eabi"
+
+@globalIntConst = constant i32 3
+@globalIntVar = global i32 5

transform/testdata/globals-non-const.out.ll

@@ -0,0 +1,5 @@
+target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "armv7em-none-eabi"
+
+@globalIntConst = global i32 3
+@globalIntVar = global i32 5