interp: fix bug in compiler-time/run-time package initializers

Make sure that if a package initializer cannot be run, later package
initializers won't try to access any global variables touched by the
uninterpretable package initializer.

Author: aykevl

interp/interp.go

@@ -116,9 +116,16 @@ func Run(mod llvm.Module, debug bool) error {
 				if r.debug {
 					fmt.Fprintln(os.Stderr, "not interpreting", r.pkgName, "because of error:", callErr.Error())
 				}
+				// Remove instructions that were created as part of interpreting
+				// the package.
 				mem.revert()
+				// Create a call to the package initializer (which was
+				// previously deleted).
 				i8undef := llvm.Undef(r.i8ptrType)
 				r.builder.CreateCall(fn, []llvm.Value{i8undef, i8undef}, "")
+				// Make sure that any globals touched by the package
+				// initializer, won't be accessed by later package initializers.
+				r.markExternalLoad(fn)
 				continue
 			}
 			return callErr
@@ -272,3 +279,19 @@ func (r *runner) getFunction(llvmFn llvm.Value) *function {
 	r.functionCache[llvmFn] = fn
 	return fn
 }
+
+// markExternalLoad marks the given llvmValue as being loaded externally. This
+// is primarily used to mark package initializers that could not be run at
+// compile time. As an example, a package initialize might store to a global
+// variable. Another package initializer might read from the same global
+// variable. By marking this function as being run at runtime, that load
+// instruction will need to be run at runtime instead of at compile time.
+func (r *runner) markExternalLoad(llvmValue llvm.Value) {
+	mem := memoryView{r: r}
+	mem.markExternalLoad(llvmValue)
+	for index, obj := range mem.objects {
+		if obj.marked > r.objects[index].marked {
+			r.objects[index].marked = obj.marked
+		}
+	}
+}

interp/testdata/revert.ll

@@ -3,17 +3,28 @@ target triple = "x86_64--linux"
 
 declare void @externalCall(i64)
 
+@foo.knownAtRuntime = global i64 0
+@bar.knownAtRuntime = global i64 0
+
 define void @runtime.initAll() unnamed_addr {
 entry:
   call void @foo.init(i8* undef, i8* undef)
+  call void @bar.init(i8* undef, i8* undef)
   call void @main.init(i8* undef, i8* undef)
   ret void
 }
 
 define internal void @foo.init(i8* %context, i8* %parentHandle) unnamed_addr {
+  store i64 5, i64* @foo.knownAtRuntime
   unreachable ; this triggers a revert of @foo.init.
 }
 
+define internal void @bar.init(i8* %context, i8* %parentHandle) unnamed_addr {
+  %val = load i64, i64* @foo.knownAtRuntime
+  store i64 %val, i64* @bar.knownAtRuntime
+  ret void
+}
+
 define internal void @main.init(i8* %context, i8* %parentHandle) unnamed_addr {
 entry:
   call void @externalCall(i64 3)

interp/testdata/revert.out.ll

@@ -1,15 +1,21 @@
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64--linux"
 
+@foo.knownAtRuntime = local_unnamed_addr global i64 0
+@bar.knownAtRuntime = local_unnamed_addr global i64 0
+
 declare void @externalCall(i64) local_unnamed_addr
 
 define void @runtime.initAll() unnamed_addr {
 entry:
   call fastcc void @foo.init(i8* undef, i8* undef)
+  %val = load i64, i64* @foo.knownAtRuntime, align 8
+  store i64 %val, i64* @bar.knownAtRuntime, align 8
   call void @externalCall(i64 3)
   ret void
 }
 
 define internal fastcc void @foo.init(i8* %context, i8* %parentHandle) unnamed_addr {
+  store i64 5, i64* @foo.knownAtRuntime, align 8
   unreachable
 }