From b0604f2a977b7262ff702923f95b449f2bda238f Mon Sep 17 00:00:00 2001
From: Jeffrey Tan <jeffreytan@fb.com>
Date: Fri, 17 Jun 2016 15:11:56 -0700
Subject: [PATCH] Nuclide xdebug async stepping (1/N) -- Refactor stack depth
 disposition logic

Summary: Make it easier for reuse by async stepping later.

Reviewed By: alexmalyshev

Differential Revision: D3406171

fbshipit-source-id: 2a20fc2e99e093d95e837540a3a018dd73c05818
---
 hphp/runtime/vm/debugger-hook.cpp | 21 +++++++++++++++++----
 hphp/runtime/vm/debugger-hook.h   |  8 ++++++++
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/hphp/runtime/vm/debugger-hook.cpp b/hphp/runtime/vm/debugger-hook.cpp
index f3bb1c6a430..5cbb5791e55 100644
--- a/hphp/runtime/vm/debugger-hook.cpp
+++ b/hphp/runtime/vm/debugger-hook.cpp
@@ -176,6 +176,8 @@ void phpDebuggerOpcodeHook(const unsigned char* pc) {
     req_data.clearActiveLineBreak();
   }
 
+  auto curStackDisp = getStackDisposition(req_data.getDebuggerFlowDepth());
+
   // Check if the step in command is active. Special case builtins because they
   // are meaningless to the user
   if (UNLIKELY(req_data.getDebuggerStepIn() && !func->isBuiltin())) {
@@ -184,8 +186,7 @@ void phpDebuggerOpcodeHook(const unsigned char* pc) {
       // Next command is not active, just break.
       hook->onStepInBreak(unit, line);
       return;
-    } else if (req_data.getDebuggerStackDepth() <=
-                req_data.getDebuggerFlowDepth()) {
+    } else if (curStackDisp != StackDepthDisposition::Deeper) {
       // Next command is active but we didn't step in. We are done.
       req_data.setDebuggerNext(false);
       hook->onNextBreak(unit, line);
@@ -207,7 +208,7 @@ void phpDebuggerOpcodeHook(const unsigned char* pc) {
   // original, then we skip over the PopR opcode if it exists and then break
   // (matching hphpd).
   if (UNLIKELY(req_data.getDebuggerStepOut() == StepOutState::Out &&
-      req_data.getDebuggerStackDepth() < req_data.getDebuggerFlowDepth() &&
+      curStackDisp == StackDepthDisposition::Shallower &&
       peek_op(pc) != OpPopR)) {
     req_data.setDebuggerStepOut(StepOutState::None);
     if (!req_data.getDebuggerNext()) {
@@ -244,6 +245,17 @@ void phpDebuggerOpcodeHook(const unsigned char* pc) {
   TRACE(5, "out phpDebuggerOpcodeHook()\n");
 }
 
+StackDepthDisposition getStackDisposition(int baseline) {
+  auto& req_data = RID();
+  auto curStackDepth = req_data.getDebuggerStackDepth();
+  if (curStackDepth > baseline) {
+    return StackDepthDisposition::Deeper;
+  } else if (curStackDepth < baseline) {
+    return StackDepthDisposition::Shallower;
+  }
+  return StackDepthDisposition::Equal;
+}
+
 // Hook called on request start before main() is invoked
 void phpDebuggerRequestInitHook() {
   getDebuggerHook()->onRequestInit();
@@ -269,8 +281,9 @@ void phpDebuggerFuncExitHook(const ActRec* ar) {
 
   // If the step out command is active and if our stack depth has decreased,
   // we are out of the function being stepped out of
+  auto baseline = req_data.getDebuggerFlowDepth();
   if (UNLIKELY(req_data.getDebuggerStepOut() == StepOutState::Stepping &&
-      req_data.getDebuggerStackDepth() < req_data.getDebuggerFlowDepth())) {
+      getStackDisposition(baseline) == StackDepthDisposition::Shallower)) {
       req_data.setDebuggerStepOut(StepOutState::Out);
   }
 }
diff --git a/hphp/runtime/vm/debugger-hook.h b/hphp/runtime/vm/debugger-hook.h
index 29602578ef4..418bb082c13 100644
--- a/hphp/runtime/vm/debugger-hook.h
+++ b/hphp/runtime/vm/debugger-hook.h
@@ -62,6 +62,12 @@ bool isHphpd(const DebuggerHook*);
 // debugger interrupts for every opcode executed (modulo filters.)
 #define DEBUGGER_FORCE_INTR (RID().getDebuggerForceIntr())
 
+enum class StackDepthDisposition {
+  Equal,        // Same.
+  Shallower,    // Less than baseline.
+  Deeper,       // Greater than baseline.
+};
+
 ////////////////////////////////////////////////////////////////////////////////
 // DebuggerHook
 // A hook for debugger events.  Any extension can subclass this class and
@@ -243,6 +249,8 @@ void phpRemoveBreakPointLine(const Unit* unit, int line);
 
 bool phpHasBreakpoint(const Unit* unit, Offset offset);
 
+StackDepthDisposition getStackDisposition(int baseline);
+
 }
 
 #endif
-- 
2.11.4.GIT