diff --git a/interp/frame.go b/interp/frame.go
index 16984f93f4..90cee4a194 100644
--- a/interp/frame.go
+++ b/interp/frame.go
@@ -92,7 +92,8 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 		case !inst.IsALoadInst().IsNil():
 			operand := fr.getLocal(inst.Operand(0)).(*LocalValue)
 			var value llvm.Value
-			if !operand.IsConstant() || inst.IsVolatile() || (!operand.Underlying.IsAConstantExpr().IsNil() && operand.Underlying.Opcode() == llvm.BitCast) {
+			if inst.IsVolatile() || fr.Eval.isDirty(operand.Value()) {
+				fr.Eval.markDirty(operand.Value())
 				value = fr.builder.CreateLoad(operand.Value(), inst.Name())
 			} else {
 				var err error
@@ -108,7 +109,8 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 		case !inst.IsAStoreInst().IsNil():
 			value := fr.getLocal(inst.Operand(0))
 			ptr := fr.getLocal(inst.Operand(1))
-			if inst.IsVolatile() {
+			if inst.IsVolatile() || fr.Eval.isDirty(ptr.Value()) {
+				fr.Eval.markDirty(ptr.Value())
 				fr.builder.CreateStore(value.Value(), ptr.Value())
 			} else {
 				err := ptr.Store(value.Value())
diff --git a/interp/interp.go b/interp/interp.go
index d5ff396568..fe09d21b7d 100644
--- a/interp/interp.go
+++ b/interp/interp.go
@@ -136,26 +136,27 @@ func (e *Eval) getValue(v llvm.Value) Value {
 // markDirty marks the passed-in LLVM value dirty, recursively. For example,
 // when it encounters a constant GEP on a global, it marks the global dirty.
 func (e *Eval) markDirty(v llvm.Value) {
-	if !v.IsAGlobalVariable().IsNil() {
-		if v.IsGlobalConstant() {
-			return
-		}
-		if _, ok := e.dirtyGlobals[v]; !ok {
-			e.dirtyGlobals[v] = struct{}{}
-			e.sideEffectFuncs = nil // re-calculate all side effects
-		}
-	} else if v.IsConstant() {
-		if v.OperandsCount() >= 2 && !v.Operand(0).IsAGlobalVariable().IsNil() {
-			// looks like a constant getelementptr of a global.
-			// TODO: find a way to make sure it really is: v.Opcode() returns 0.
-			e.markDirty(v.Operand(0))
+	if v.Type().TypeKind() != llvm.PointerTypeKind {
+		return
+	}
+	v = unwrap(v)
+	if v.IsAGlobalVariable().IsNil() {
+		if !v.IsAUndefValue().IsNil() || !v.IsAConstantPointerNull().IsNil() {
+			// Nothing to mark here: these definitely don't point to globals.
 			return
 		}
-		return // nothing to mark
-	} else if !v.IsAGetElementPtrInst().IsNil() {
-		panic("interp: todo: GEP")
-	} else {
-		// Not constant and not a global or GEP so doesn't have to be marked
-		// non-constant.
+		panic("interp: trying to mark a non-global as dirty")
+	}
+	e.dirtyGlobals[v] = struct{}{}
+}
+
+// isDirty returns whether the value is tracked as part of the set of dirty
+// globals or not. If it's not dirty, it means loads/stores can be done at
+// compile time.
+func (e *Eval) isDirty(v llvm.Value) bool {
+	v = unwrap(v)
+	if _, ok := e.dirtyGlobals[v]; ok {
+		return true
 	}
+	return false
 }
diff --git a/interp/utils.go b/interp/utils.go
index c115477133..4903e30205 100644
--- a/interp/utils.go
+++ b/interp/utils.go
@@ -106,21 +106,22 @@ func isZero(v llvm.Value) (result bool, ok bool) {
 	return false, false // not valid
 }
 
-// unwrap returns the underlying value, with GEPs removed. This can be useful to
-// get the underlying global of a GEP pointer.
+// unwrap returns the underlying global value, with GEPs and bitcasts removed.
+// This can be useful to get the underlying global of a GEP pointer.
 func unwrap(value llvm.Value) llvm.Value {
-	for {
-		if !value.IsAConstantExpr().IsNil() {
-			switch value.Opcode() {
-			case llvm.GetElementPtr:
-				value = value.Operand(0)
-				continue
-			}
-		} else if !value.IsAGetElementPtrInst().IsNil() {
-			value = value.Operand(0)
-			continue
-		}
-		break
+	var opcode llvm.Opcode
+	if !value.IsAConstantExpr().IsNil() {
+		opcode = value.Opcode()
+	} else if !value.IsAInstruction().IsNil() {
+		opcode = value.InstructionOpcode()
+	} else {
+		return value
+	}
+	switch opcode {
+	case llvm.BitCast, llvm.GetElementPtr, llvm.PtrToInt:
+		// Make sure dirty globals are caught through pointer casts.
+		return unwrap(value.Operand(0))
+	default:
+		return value
 	}
-	return value
 }
diff --git a/interp/values.go b/interp/values.go
index ae29bf99d2..493d35361a 100644
--- a/interp/values.go
+++ b/interp/values.go
@@ -37,7 +37,7 @@ func (v *LocalValue) Type() llvm.Type {
 }
 
 func (v *LocalValue) IsConstant() bool {
-	if _, ok := v.Eval.dirtyGlobals[unwrap(v.Underlying)]; ok {
+	if v.Eval.isDirty(v.Underlying) {
 		return false
 	}
 	return v.Underlying.IsConstant()
@@ -45,6 +45,11 @@ func (v *LocalValue) IsConstant() bool {
 
 // Load loads a constant value if this is a constant pointer.
 func (v *LocalValue) Load() (llvm.Value, error) {
+	if v.Eval.isDirty(v.Underlying) {
+		// This may indicate a bug elsewhere.
+		v.MarkDirty()
+		return v.Eval.builder.CreateLoad(v.Underlying, ""), nil
+	}
 	if !v.Underlying.IsAGlobalVariable().IsNil() {
 		return v.Underlying.Initializer(), nil
 	}
@@ -52,7 +57,8 @@ func (v *LocalValue) Load() (llvm.Value, error) {
 	case llvm.GetElementPtr:
 		indices := v.getConstGEPIndices()
 		if indices[0] != 0 {
-			return llvm.Value{}, errors.New("invalid GEP")
+			v.MarkDirty()
+			return v.Eval.builder.CreateLoad(v.Underlying, ""), nil
 		}
 		global := v.Eval.getValue(v.Underlying.Operand(0))
 		agg, err := global.Load()
@@ -61,9 +67,35 @@ func (v *LocalValue) Load() (llvm.Value, error) {
 		}
 		return llvm.ConstExtractValue(agg, indices[1:]), nil
 	case llvm.BitCast:
-		return llvm.Value{}, errors.New("interp: load from a bitcast")
+		// Assuming a pointer bitcast, such as i64* to double*.
+		// By loading the pre-bitcast value and then bitcasting the loaded value
+		// we work around the problem.
+		sourceType := v.Underlying.Operand(0).Type().ElementType()
+		destType := v.Underlying.Type().ElementType()
+		if v.Eval.TargetData.TypeAllocSize(sourceType) != v.Eval.TargetData.TypeAllocSize(destType) {
+			v.MarkDirty()
+			return v.Eval.builder.CreateLoad(v.Underlying, ""), nil
+		}
+		if !isScalar(sourceType) || !isScalar(destType) {
+			// Actually bitcasts are a bit more flexible than this: any
+			// non-aggregate first-class type can be casted.
+			v.MarkDirty()
+			return v.Eval.builder.CreateLoad(v.Underlying, ""), nil
+		}
+		valueBeforeCast := LocalValue{v.Eval, v.Underlying.Operand(0)}
+		llvmValueBeforeCast, err := valueBeforeCast.Load()
+		if err != nil {
+			return llvm.Value{}, err
+		}
+		if !llvmValueBeforeCast.IsConstant() {
+			// Unlikely but check for it anyway.
+			v.MarkDirty()
+			return v.Eval.builder.CreateLoad(v.Underlying, ""), nil
+		}
+		return llvm.ConstBitCast(llvmValueBeforeCast, destType), nil
 	default:
-		return llvm.Value{}, errors.New("interp: load from a constant")
+		v.MarkDirty()
+		return v.Eval.builder.CreateLoad(v.Underlying, ""), nil
 	}
 }
 
@@ -161,14 +193,7 @@ func (v *LocalValue) getConstGEPIndices() []uint32 {
 // MarkDirty marks this global as dirty, meaning that every load from and store
 // to this global (from now on) must be performed at runtime.
 func (v *LocalValue) MarkDirty() {
-	underlying := unwrap(v.Underlying)
-	if underlying.IsAGlobalVariable().IsNil() {
-		panic("trying to mark a non-global as dirty")
-	}
-	if !v.IsConstant() {
-		return // already dirty
-	}
-	v.Eval.dirtyGlobals[underlying] = struct{}{}
+	v.Eval.markDirty(v.Underlying)
 }
 
 // MapValue implements a Go map which is created at compile time and stored as a