[wasm] Add flag to validate asm.js modules.

src/compiler.cc

Index: src/compiler.cc
diff --git a/src/compiler.cc b/src/compiler.cc
index 6885b55e31e32aa71859b39f334bf6db83f8fc26..fc9e0a66afca9384e4f31a9e80fff39a7b422873 100644
--- a/src/compiler.cc
+++ b/src/compiler.cc
@@ -30,6 +30,7 @@
 #include "src/profiler/cpu-profiler.h"
 #include "src/runtime-profiler.h"
 #include "src/snapshot/code-serializer.h"
+#include "src/typing-asm.h"
 #include "src/vm-state-inl.h"
 
 namespace v8 {
@@ -464,6 +465,17 @@ int CodeAndMetadataSize(CompilationInfo* info) {
 bool GenerateUnoptimizedCode(CompilationInfo* info) {
   bool success;
   EnsureFeedbackVector(info);

[bradnelson, 2016/05/12 09:03:59]

I've been thrashing about a bit attempting to craft a similar CL.
I'd vacillated if this was a good place to glue things in, thanks. :-)

One issue with this spot (and several others), is that the AST is lazy here
(doesn't have child function bodies).
The typer currently requires this, which of course won't do in terms of memory
footprint.

My intention is to have it selectively parse these, but wasn't sure if that
belongs in the typer, or external to it, curious what you guys think?

As near as I can tell, assuming I don't keep the full AST in memory, two parses
/ passes through each function will be required which is a shame. The first is
needed to gather up function signatures (which touches very little of the AST),
the second to actually type the function (which could also be done in tandem
with asm->wasm for the function).

+  if (FLAG_validate_asm && info->scope()->asm_module()) {
+    AsmTyper typer(info->isolate(), info->zone(), *(info->script()),
+                   info->literal());
+    if (FLAG_enable_simd_asmjs) {
+      typer.set_allow_simd(true);
+    }
+    if (!typer.Validate()) {
+      DCHECK(!info->isolate()->has_pending_exception());

[bradnelson, 2016/05/12 09:03:59]

My intention was that in the failure case the TypingResetter gets run on the
AST, as the asm typer leaves behind partial type info (that can be wrong in the
failure case). Also some of the backends (crankshaft anyway) don't like having
types set.
Or maybe reseting the AST types should get called/folded into AsmTyper?

In any event, I plan to swap out using types.h types on the AST for something
outside the AST real soon, so likely moot.

+      PrintF("Validation of asm.js module failed: %s", typer.error_message());
+    }
+  }
   if (FLAG_ignition && UseIgnition(info)) {
     success = interpreter::Interpreter::MakeBytecode(info);
   } else {