[Clang] Fix segmentation fault caused by VarBypassDetector stack overflow on deeply nested expressions (#124128)

This happens when using `-O2`.

Similarly to #111701
([test](https://github.com/bricknerb/llvm-project/blob/93e4a7386ec897e53d7330c6206d38759a858be2/clang/test/CodeGen/deeply-nested-expressions.cpp)),
not adding a test that reproduces since this test is slow and likely to
be hard to maintained as discussed here and in [previous
discussion](https://github.com/llvm/llvm-project/pull/111701/files/1a63281b6c240352653fd2e4299755c1f32a76f4#r1795518779).
Test that was reverted here:
d6b5576

Author: bricknerb

clang/lib/CodeGen/CodeGenFunction.cpp

@@ -1534,7 +1534,7 @@ void CodeGenFunction::GenerateCode(GlobalDecl GD, llvm::Function *Fn,
     // Initialize helper which will detect jumps which can cause invalid
     // lifetime markers.
     if (ShouldEmitLifetimeMarkers)
-      Bypasses.Init(Body);
+      Bypasses.Init(CGM, Body);
   }
 
   // Emit the standard function prologue.

clang/lib/CodeGen/VarBypassDetector.cpp

@@ -8,6 +8,7 @@
 
 #include "VarBypassDetector.h"
 
+#include "CodeGenModule.h"
 #include "clang/AST/Decl.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/Stmt.h"
@@ -17,21 +18,21 @@ using namespace CodeGen;
 
 /// Clear the object and pre-process for the given statement, usually function
 /// body statement.
-void VarBypassDetector::Init(const Stmt *Body) {
+void VarBypassDetector::Init(CodeGenModule &CGM, const Stmt *Body) {
   FromScopes.clear();
   ToScopes.clear();
   Bypasses.clear();
   Scopes = {{~0U, nullptr}};
   unsigned ParentScope = 0;
-  AlwaysBypassed = !BuildScopeInformation(Body, ParentScope);
+  AlwaysBypassed = !BuildScopeInformation(CGM, Body, ParentScope);
   if (!AlwaysBypassed)
     Detect();
 }
 
 /// Build scope information for a declaration that is part of a DeclStmt.
 /// Returns false if we failed to build scope information and can't tell for
 /// which vars are being bypassed.
-bool VarBypassDetector::BuildScopeInformation(const Decl *D,
+bool VarBypassDetector::BuildScopeInformation(CodeGenModule &CGM, const Decl *D,
                                               unsigned &ParentScope) {
   const VarDecl *VD = dyn_cast<VarDecl>(D);
   if (VD && VD->hasLocalStorage()) {
@@ -41,7 +42,7 @@ bool VarBypassDetector::BuildScopeInformation(const Decl *D,
 
   if (const VarDecl *VD = dyn_cast<VarDecl>(D))
     if (const Expr *Init = VD->getInit())
-      return BuildScopeInformation(Init, ParentScope);
+      return BuildScopeInformation(CGM, Init, ParentScope);
 
   return true;
 }
@@ -50,7 +51,7 @@ bool VarBypassDetector::BuildScopeInformation(const Decl *D,
 /// LabelAndGotoScopes and recursively walking the AST as needed.
 /// Returns false if we failed to build scope information and can't tell for
 /// which vars are being bypassed.
-bool VarBypassDetector::BuildScopeInformation(const Stmt *S,
+bool VarBypassDetector::BuildScopeInformation(CodeGenModule &CGM, const Stmt *S,
                                               unsigned &origParentScope) {
   // If this is a statement, rather than an expression, scopes within it don't
   // propagate out into the enclosing scope. Otherwise we have to worry about
@@ -68,12 +69,12 @@ bool VarBypassDetector::BuildScopeInformation(const Stmt *S,
 
   case Stmt::SwitchStmtClass:
     if (const Stmt *Init = cast<SwitchStmt>(S)->getInit()) {
-      if (!BuildScopeInformation(Init, ParentScope))
+      if (!BuildScopeInformation(CGM, Init, ParentScope))
         return false;
       ++StmtsToSkip;
     }
     if (const VarDecl *Var = cast<SwitchStmt>(S)->getConditionVariable()) {
-      if (!BuildScopeInformation(Var, ParentScope))
+      if (!BuildScopeInformation(CGM, Var, ParentScope))
         return false;
       ++StmtsToSkip;
     }
@@ -86,7 +87,7 @@ bool VarBypassDetector::BuildScopeInformation(const Stmt *S,
   case Stmt::DeclStmtClass: {
     const DeclStmt *DS = cast<DeclStmt>(S);
     for (auto *I : DS->decls())
-      if (!BuildScopeInformation(I, origParentScope))
+      if (!BuildScopeInformation(CGM, I, origParentScope))
         return false;
     return true;
   }
@@ -126,7 +127,11 @@ bool VarBypassDetector::BuildScopeInformation(const Stmt *S,
     }
 
     // Recursively walk the AST.
-    if (!BuildScopeInformation(SubStmt, ParentScope))
+    bool Result;
+    CGM.runWithSufficientStackSpace(S->getEndLoc(), [&] {
+      Result = BuildScopeInformation(CGM, SubStmt, ParentScope);
+    });
+    if (!Result)
       return false;
   }
   return true;

clang/lib/CodeGen/VarBypassDetector.h

@@ -14,6 +14,7 @@
 #ifndef LLVM_CLANG_LIB_CODEGEN_VARBYPASSDETECTOR_H
 #define LLVM_CLANG_LIB_CODEGEN_VARBYPASSDETECTOR_H
 
+#include "CodeGenModule.h"
 #include "clang/AST/Decl.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/DenseSet.h"
@@ -50,7 +51,7 @@ class VarBypassDetector {
   bool AlwaysBypassed = false;
 
 public:
-  void Init(const Stmt *Body);
+  void Init(CodeGenModule &CGM, const Stmt *Body);
 
   /// Returns true if the variable declaration was by bypassed by any goto or
   /// switch statement.
@@ -59,8 +60,10 @@ class VarBypassDetector {
   }
 
 private:
-  bool BuildScopeInformation(const Decl *D, unsigned &ParentScope);
-  bool BuildScopeInformation(const Stmt *S, unsigned &origParentScope);
+  bool BuildScopeInformation(CodeGenModule &CGM, const Decl *D,
+                             unsigned &ParentScope);
+  bool BuildScopeInformation(CodeGenModule &CGM, const Stmt *S,
+                             unsigned &origParentScope);
   void Detect();
   void Detect(unsigned From, unsigned To);
 };