[analysis] Add a new iterable CFG utility (#5712)

Add a new "analysis" source directory that will contain the source for a new
static program analysis framework. To start the framework, add a CFG utility
that provides convenient iterators for iterating through the basic blocks of the
CFG as well as the predecessors, successors, and contents of each block.

The new CFGs are constructed using the existing CFGWalker, but they are
different in that the new utility is meant to provide a usable representation of
a CFG whereas CFGWalker is meant to allow collecting arbitrary information about
each basic block in a CFG.

For testing and debugging purposes, add `print` methods to CFGs and basic
blocks. This requires exposing the ability to print expression contents
excluding children, which was something we previously did only for StackIR.

Also add a new gtest file with a test for constructing and printing a CFG. The
test reveals some strange properties of the current CFG construction, including
empty blocks and strange placement of `loop` instructions, but fixing these
problems is left as future work.

1 files changed, 9 insertions, 0 deletions

diff --git a/src/wasm.h b/src/wasm.h
index 474497847..727c9ca30 100644
--- a/src/wasm.h
+++ b/src/wasm.h
@@ -2308,8 +2308,16 @@ public:
   void clearDebugInfo();
 };
 
+// Utility for printing an expression with named types.
 using ModuleExpression = std::pair<Module&, Expression*>;
 
+// Utility for printing only the top level of an expression. Named types will be
+// used if `module` is non-null.
+struct ShallowExpression {
+  Expression* expr;
+  Module* module = nullptr;
+};
+
 } // namespace wasm
 
 namespace std {
@@ -2322,6 +2330,7 @@ template<> struct hash<wasm::Address> {
 std::ostream& operator<<(std::ostream& o, wasm::Module& module);
 std::ostream& operator<<(std::ostream& o, wasm::Expression& expression);
 std::ostream& operator<<(std::ostream& o, wasm::ModuleExpression pair);
+std::ostream& operator<<(std::ostream& o, wasm::ShallowExpression expression);
 std::ostream& operator<<(std::ostream& o, wasm::StackInst& inst);
 std::ostream& operator<<(std::ostream& o, wasm::StackIR& ir);