Stop to emit code if rewrite failed(failed == true)

If rewriter encounter a situation which can't be handled. It will set
the `failed` to `true`. In this situation, just stop to emit code. And
also don't check some assert.

src/asm_writing/rewriter.cpp

@@ -448,8 +448,10 @@ void Rewriter::_getAttr(RewriterVar* result, RewriterVar* ptr, int offset, Locat
 
     ptr->bumpUseEarlyIfPossible();
 
+    if (!failed) {
         assembler::Register newvar_reg = result->initializeInReg(dest);
         assembler->mov_generic(assembler::Indirect(ptr_reg, offset), newvar_reg, type);
+    }
 
     result->releaseIfNoUses();
 
@@ -2171,7 +2173,7 @@ assembler::Register RewriterVar::initializeInReg(Location l) {
 
     // Add this to vars_by_locations
     RewriterVar*& var = rewriter->vars_by_location[l];
-    assert(!var);
+    assert(!var || rewriter->failed);
     var = this;
 
     // Add the location to this

src/asm_writing/rewriter.h

@@ -577,6 +577,9 @@ protected:
     void _callOptimalEncoding(assembler::Register tmp_reg, void* func_addr);
 
     void assertConsistent() {
+
+        if (failed)
+            return;
 #ifndef NDEBUG
         for (RewriterVar& var : vars) {
             for (Location l : var.locations) {