[Wasm RyuJIT] Wasm control flow basics (#121417)

Determine how to emit Wasm control flow from the JIT's control flow
graph.

Relies on loop-aware RPO to determine the block order. Currently only
handles the main method. Assumes irreducible loops have been fixed
upstream (which is not yet guaranteed; bails out if not so).

Doesn't actually do any emission, just prints a textual description in
the JIT dump (along with a dot markup version).

Uses only LOOP and BLOCK. Tries to limit the extent of BLOCK.

Run for now as an optional phase even if not targeting Wasm, to do some
stress testing.

Contributes to #121178

Author: AndyAyersMS

src/coreclr/jit/CMakeLists.txt

@@ -115,6 +115,7 @@ set( JIT_SOURCES
   fgprofile.cpp
   fgprofilesynthesis.cpp
   fgstmt.cpp
+  fgwasm.cpp
   flowgraph.cpp
   forwardsub.cpp
   gcinfo.cpp

src/coreclr/jit/compiler.cpp

@@ -5016,6 +5016,16 @@ void Compiler::compCompile(void** methodCodePtr, uint32_t* methodCodeSize, JitFl
     DoPhase(this, PHASE_ALIGN_LOOPS, &Compiler::placeLoopAlignInstructions);
 #endif
 
+#ifdef DEBUG
+    // Optionally, simulate generating wasm control flow
+    // (eventually this will become part of the wasm target)
+    //
+    if (JitConfig.JitWasmControlFlow() > 0)
+    {
+        DoPhase(this, PHASE_WASM_CONTROL_FLOW, &Compiler::fgWasmControlFlow);
+    }
+#endif
+
     // The common phase checks and dumps are no longer relevant past this point.
     //
     activePhaseChecks = PhaseChecks::CHECK_NONE;

src/coreclr/jit/compiler.h

@@ -6237,6 +6237,8 @@ class Compiler
 
     PhaseStatus fgFindOperOrder();
 
+    PhaseStatus fgWasmControlFlow();
+
     // method that returns if you should split here
     typedef bool(fgSplitPredicate)(GenTree* tree, GenTree* parent, fgWalkData* data);
 

src/coreclr/jit/compmemkind.h

@@ -68,6 +68,7 @@ CompMemKindMacro(MaskConversionOpt)
 CompMemKindMacro(TryRegionClone)
 CompMemKindMacro(Async)
 CompMemKindMacro(RangeCheckCloning)
+CompMemKindMacro(WasmCfgLowering)
 //clang-format on
 
 #undef CompMemKindMacro

src/coreclr/jit/compphases.h

@@ -122,6 +122,8 @@ CompPhaseNameMacro(PHASE_RATIONALIZE,                "Rationalize IR",
 CompPhaseNameMacro(PHASE_REPAIR_PROFILE_POST_MORPH,  "Repair profile post-morph",      false, -1, false)
 CompPhaseNameMacro(PHASE_REPAIR_PROFILE_PRE_LAYOUT,  "Repair profile pre-layout",      false, -1, false)
 
+CompPhaseNameMacro(PHASE_WASM_CONTROL_FLOW,          "Wasm control flow",              false, -1, false)
+
 CompPhaseNameMacro(PHASE_ASYNC,                      "Transform async",                false, -1, true)
 CompPhaseNameMacro(PHASE_LCLVARLIVENESS,             "Local var liveness",             true,  -1, false)
 CompPhaseNameMacro(PHASE_LCLVARLIVENESS_INIT,        "Local var liveness init",        false, PHASE_LCLVARLIVENESS, false)