Improve behavior in the case of stack exhaustion.

Summary:
Clang performs various recursive operations (such as template instantiation),
and may use non-trivial amounts of stack space in each recursive step (for
instance, due to recursive AST walks). While we try to keep the stack space
used by such steps to a minimum and we have explicit limits on the number of
such steps we perform, it's impractical to guarantee that we won't blow out the
stack on deeply recursive template instantiations on complex ASTs, even with
only a moderately high instantiation depth limit.

The user experience in these cases is generally terrible: we crash with
no hint of what went wrong. Under this patch, we attempt to do better:

 * Detect when the stack is nearly exhausted, and produce a warning with a
   nice template instantiation backtrace, telling the user that we might
   run slowly or crash.

 * For cases where we're forced to trigger recursive template
   instantiation in arbitrarily-deeply-nested contexts, check whether
   we're nearly out of stack space and allocate a new stack (by spawning
   a new thread) after producing the warning.

Reviewers: rnk, aaron.ballman

Subscribers: mgorny, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D66361

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@369940 91177308-0d34-0410-b5e6-96231b3b80d8

12 files changed, 276 insertions, 121 deletions

diff --git a/lib/Basic/CMakeLists.txt b/lib/Basic/CMakeLists.txt
index b4d6ced4d5..be739c7046 100644
--- a/lib/Basic/CMakeLists.txt
+++ b/lib/Basic/CMakeLists.txt
@@ -60,6 +60,7 @@ add_clang_library(clangBasic
   Sanitizers.cpp
   SourceLocation.cpp
   SourceManager.cpp
+  Stack.cpp
   TargetInfo.cpp
   Targets.cpp
   Targets/AArch64.cpp
diff --git a/lib/Basic/Stack.cpp b/lib/Basic/Stack.cpp
new file mode 100644
index 0000000000..667db5c51f
--- /dev/null
+++ b/lib/Basic/Stack.cpp
@@ -0,0 +1,71 @@
+//===--- Stack.h - Utilities for dealing with stack space -------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Defines utilities for dealing with stack allocation and stack space.
+///
+//===----------------------------------------------------------------------===//
+
+#include "clang/Basic/Stack.h"
+#include "llvm/ADT/Optional.h"
+#include "llvm/Support/CrashRecoveryContext.h"
+
+static LLVM_THREAD_LOCAL void *BottomOfStack = nullptr;
+
+static void *getStackPointer() {
+#if __GNUC__ || __has_builtin(__builtin_frame_address)
+  return __builtin_frame_address(0);
+#elif defined(_MSC_VER)
+  return _AddressOfReturnAddress();
+#else
+  char CharOnStack = 0;
+  // The volatile store here is intended to escape the local variable, to
+  // prevent the compiler from optimizing CharOnStack into anything other
+  // than a char on the stack.
+  //
+  // Tested on: MSVC 2015 - 2019, GCC 4.9 - 9, Clang 3.2 - 9, ICC 13 - 19.
+  char *volatile Ptr = &CharOnStack;
+  return Ptr;
+#endif
+}
+
+void clang::noteBottomOfStack() {
+  if (!BottomOfStack)
+    BottomOfStack = getStackPointer();
+}
+
+bool clang::isStackNearlyExhausted() {
+  // We consider 256 KiB to be sufficient for any code that runs between checks
+  // for stack size.
+  constexpr size_t SufficientStack = 256 << 10;
+
+  // If we don't know where the bottom of the stack is, hope for the best.
+  if (!BottomOfStack)
+    return false;
+
+  intptr_t StackDiff = (intptr_t)getStackPointer() - (intptr_t)BottomOfStack;
+  size_t StackUsage = (size_t)std::abs(StackDiff);
+
+  // If the stack pointer has a surprising value, we do not understand this
+  // stack usage scheme. (Perhaps the target allocates new stack regions on
+  // demand for us.) Don't try to guess what's going on.
+  if (StackUsage > DesiredStackSize)
+    return false;
+
+  return StackUsage >= DesiredStackSize - SufficientStack;
+}
+
+void clang::runWithSufficientStackSpaceSlow(llvm::function_ref<void()> Diag,
+                                            llvm::function_ref<void()> Fn) {
+  llvm::CrashRecoveryContext CRC;
+  CRC.RunSafelyOnThread([&] {
+    noteBottomOfStack();
+    Diag();
+    Fn();
+  }, DesiredStackSize);
+}
diff --git a/lib/Frontend/CompilerInstance.cpp b/lib/Frontend/CompilerInstance.cpp
index cbf519758e..f0227d0501 100644
--- a/lib/Frontend/CompilerInstance.cpp
+++ b/lib/Frontend/CompilerInstance.cpp
@@ -890,6 +890,11 @@ bool CompilerInstance::ExecuteAction(FrontendAction &Act) {
   assert(!getFrontendOpts().ShowHelp && "Client must handle '-help'!");
   assert(!getFrontendOpts().ShowVersion && "Client must handle '-version'!");
 
+  // Mark this point as the bottom of the stack if we don't have somewhere
+  // better. We generally expect frontend actions to be invoked with (nearly)
+  // DesiredStackSpace available.
+  noteBottomOfStack();
+
   // FIXME: Take this as an argument, once all the APIs we used have moved to
   // taking it as an input instead of hard-coding llvm::errs.
   raw_ostream &OS = llvm::errs();
diff --git a/lib/Sema/Sema.cpp b/lib/Sema/Sema.cpp
index 17b414556c..d4be3e9242 100644
--- a/lib/Sema/Sema.cpp
+++ b/lib/Sema/Sema.cpp
@@ -22,6 +22,7 @@
 #include "clang/AST/StmtCXX.h"
 #include "clang/Basic/DiagnosticOptions.h"
 #include "clang/Basic/PartialDiagnostic.h"
+#include "clang/Basic/Stack.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Lex/HeaderSearch.h"
 #include "clang/Lex/Preprocessor.h"
@@ -386,6 +387,19 @@ Sema::~Sema() {
   assert(DelayedTypos.empty() && "Uncorrected typos!");
 }
 
+void Sema::warnStackExhausted(SourceLocation Loc) {
+  // Only warn about this once.
+  if (!WarnedStackExhausted) {
+    Diag(Loc, diag::warn_stack_exhausted);
+    WarnedStackExhausted = true;
+  }
+}
+
+void Sema::runWithSufficientStackSpace(SourceLocation Loc,
+                                       llvm::function_ref<void()> Fn) {
+  clang::runWithSufficientStackSpace([&] { warnStackExhausted(Loc); }, Fn);
+}
+
 /// makeUnavailableInSystemHeader - There is an error in the current
 /// context.  If we're still in a system header, and we can plausibly
 /// make the relevant declaration unavailable instead of erroring, do
diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index ea72bcb259..43e61d3429 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -4832,8 +4832,10 @@ bool Sema::CheckCXXDefaultArgExpr(SourceLocation CallLoc, FunctionDecl *FD,
       //   default argument expression appears.
       ContextRAII SavedContext(*this, FD);
       LocalInstantiationScope Local(*this);
-      Result = SubstInitializer(UninstExpr, MutiLevelArgList,
-                                /*DirectInit*/false);
+      runWithSufficientStackSpace(CallLoc, [&] {
+        Result = SubstInitializer(UninstExpr, MutiLevelArgList,
+                                  /*DirectInit*/false);
+      });
     }
     if (Result.isInvalid())
       return true;
@@ -15175,6 +15177,17 @@ void Sema::MarkFunctionReferenced(SourceLocation Loc, FunctionDecl *Func,
   if (IsRecursiveCall && OdrUse == OdrUseContext::Used)
     OdrUse = OdrUseContext::FormallyOdrUsed;
 
+  // Trivial default constructors and destructors are never actually used.
+  // FIXME: What about other special members?
+  if (Func->isTrivial() && !Func->hasAttr<DLLExportAttr>() &&
+      OdrUse == OdrUseContext::Used) {
+    if (auto *Constructor = dyn_cast<CXXConstructorDecl>(Func))
+      if (Constructor->isDefaultConstructor())
+        OdrUse = OdrUseContext::FormallyOdrUsed;
+    if (isa<CXXDestructorDecl>(Func))
+      OdrUse = OdrUseContext::FormallyOdrUsed;
+  }
+
   // C++20 [expr.const]p12:
   //   A function [...] is needed for constant evaluation if it is [...] a
   //   constexpr function that is named by an expression that is potentially
@@ -15235,98 +15248,101 @@ void Sema::MarkFunctionReferenced(SourceLocation Loc, FunctionDecl *Func,
 
   // If we need a definition, try to create one.
   if (NeedDefinition && !Func->getBody()) {
-    if (CXXConstructorDecl *Constructor = dyn_cast<CXXConstructorDecl>(Func)) {
-      Constructor = cast<CXXConstructorDecl>(Constructor->getFirstDecl());
-      if (Constructor->isDefaulted() && !Constructor->isDeleted()) {
-        if (Constructor->isDefaultConstructor()) {
-          if (Constructor->isTrivial() &&
-              !Constructor->hasAttr<DLLExportAttr>())
+    runWithSufficientStackSpace(Loc, [&] {
+      if (CXXConstructorDecl *Constructor =
+              dyn_cast<CXXConstructorDecl>(Func)) {
+        Constructor = cast<CXXConstructorDecl>(Constructor->getFirstDecl());
+        if (Constructor->isDefaulted() && !Constructor->isDeleted()) {
+          if (Constructor->isDefaultConstructor()) {
+            if (Constructor->isTrivial() &&
+                !Constructor->hasAttr<DLLExportAttr>())
+              return;
+            DefineImplicitDefaultConstructor(Loc, Constructor);
+          } else if (Constructor->isCopyConstructor()) {
+            DefineImplicitCopyConstructor(Loc, Constructor);
+          } else if (Constructor->isMoveConstructor()) {
+            DefineImplicitMoveConstructor(Loc, Constructor);
+          }
+        } else if (Constructor->getInheritedConstructor()) {
+          DefineInheritingConstructor(Loc, Constructor);
+        }
+      } else if (CXXDestructorDecl *Destructor =
+                     dyn_cast<CXXDestructorDecl>(Func)) {
+        Destructor = cast<CXXDestructorDecl>(Destructor->getFirstDecl());
+        if (Destructor->isDefaulted() && !Destructor->isDeleted()) {
+          if (Destructor->isTrivial() && !Destructor->hasAttr<DLLExportAttr>())
             return;
-          DefineImplicitDefaultConstructor(Loc, Constructor);
-        } else if (Constructor->isCopyConstructor()) {
-          DefineImplicitCopyConstructor(Loc, Constructor);
-        } else if (Constructor->isMoveConstructor()) {
-          DefineImplicitMoveConstructor(Loc, Constructor);
+          DefineImplicitDestructor(Loc, Destructor);
         }
-      } else if (Constructor->getInheritedConstructor()) {
-        DefineInheritingConstructor(Loc, Constructor);
-      }
-    } else if (CXXDestructorDecl *Destructor =
-                   dyn_cast<CXXDestructorDecl>(Func)) {
-      Destructor = cast<CXXDestructorDecl>(Destructor->getFirstDecl());
-      if (Destructor->isDefaulted() && !Destructor->isDeleted()) {
-        if (Destructor->isTrivial() && !Destructor->hasAttr<DLLExportAttr>())
-          return;
-        DefineImplicitDestructor(Loc, Destructor);
+        if (Destructor->isVirtual() && getLangOpts().AppleKext)
+          MarkVTableUsed(Loc, Destructor->getParent());
+      } else if (CXXMethodDecl *MethodDecl = dyn_cast<CXXMethodDecl>(Func)) {
+        if (MethodDecl->isOverloadedOperator() &&
+            MethodDecl->getOverloadedOperator() == OO_Equal) {
+          MethodDecl = cast<CXXMethodDecl>(MethodDecl->getFirstDecl());
+          if (MethodDecl->isDefaulted() && !MethodDecl->isDeleted()) {
+            if (MethodDecl->isCopyAssignmentOperator())
+              DefineImplicitCopyAssignment(Loc, MethodDecl);
+            else if (MethodDecl->isMoveAssignmentOperator())
+              DefineImplicitMoveAssignment(Loc, MethodDecl);
+          }
+        } else if (isa<CXXConversionDecl>(MethodDecl) &&
+                   MethodDecl->getParent()->isLambda()) {
+          CXXConversionDecl *Conversion =
+              cast<CXXConversionDecl>(MethodDecl->getFirstDecl());
+          if (Conversion->isLambdaToBlockPointerConversion())
+            DefineImplicitLambdaToBlockPointerConversion(Loc, Conversion);
+          else
+            DefineImplicitLambdaToFunctionPointerConversion(Loc, Conversion);
+        } else if (MethodDecl->isVirtual() && getLangOpts().AppleKext)
+          MarkVTableUsed(Loc, MethodDecl->getParent());
       }
-      if (Destructor->isVirtual() && getLangOpts().AppleKext)
-        MarkVTableUsed(Loc, Destructor->getParent());
-    } else if (CXXMethodDecl *MethodDecl = dyn_cast<CXXMethodDecl>(Func)) {
-      if (MethodDecl->isOverloadedOperator() &&
-          MethodDecl->getOverloadedOperator() == OO_Equal) {
-        MethodDecl = cast<CXXMethodDecl>(MethodDecl->getFirstDecl());
-        if (MethodDecl->isDefaulted() && !MethodDecl->isDeleted()) {
-          if (MethodDecl->isCopyAssignmentOperator())
-            DefineImplicitCopyAssignment(Loc, MethodDecl);
-          else if (MethodDecl->isMoveAssignmentOperator())
-            DefineImplicitMoveAssignment(Loc, MethodDecl);
-        }
-      } else if (isa<CXXConversionDecl>(MethodDecl) &&
-                 MethodDecl->getParent()->isLambda()) {
-        CXXConversionDecl *Conversion =
-            cast<CXXConversionDecl>(MethodDecl->getFirstDecl());
-        if (Conversion->isLambdaToBlockPointerConversion())
-          DefineImplicitLambdaToBlockPointerConversion(Loc, Conversion);
-        else
-          DefineImplicitLambdaToFunctionPointerConversion(Loc, Conversion);
-      } else if (MethodDecl->isVirtual() && getLangOpts().AppleKext)
-        MarkVTableUsed(Loc, MethodDecl->getParent());
-    }
 
-    // Implicit instantiation of function templates and member functions of
-    // class templates.
-    if (Func->isImplicitlyInstantiable()) {
-      TemplateSpecializationKind TSK =
-          Func->getTemplateSpecializationKindForInstantiation();
-      SourceLocation PointOfInstantiation = Func->getPointOfInstantiation();
-      bool FirstInstantiation = PointOfInstantiation.isInvalid();
-      if (FirstInstantiation) {
-        PointOfInstantiation = Loc;
-        Func->setTemplateSpecializationKind(TSK, PointOfInstantiation);
-      } else if (TSK != TSK_ImplicitInstantiation) {
-        // Use the point of use as the point of instantiation, instead of the
-        // point of explicit instantiation (which we track as the actual point
-        // of instantiation). This gives better backtraces in diagnostics.
-        PointOfInstantiation = Loc;
-      }
+      // Implicit instantiation of function templates and member functions of
+      // class templates.
+      if (Func->isImplicitlyInstantiable()) {
+        TemplateSpecializationKind TSK =
+            Func->getTemplateSpecializationKindForInstantiation();
+        SourceLocation PointOfInstantiation = Func->getPointOfInstantiation();
+        bool FirstInstantiation = PointOfInstantiation.isInvalid();
+        if (FirstInstantiation) {
+          PointOfInstantiation = Loc;
+          Func->setTemplateSpecializationKind(TSK, PointOfInstantiation);
+        } else if (TSK != TSK_ImplicitInstantiation) {
+          // Use the point of use as the point of instantiation, instead of the
+          // point of explicit instantiation (which we track as the actual point
+          // of instantiation). This gives better backtraces in diagnostics.
+          PointOfInstantiation = Loc;
+        }
 
-      if (FirstInstantiation || TSK != TSK_ImplicitInstantiation ||
-          Func->isConstexpr()) {
-        if (isa<CXXRecordDecl>(Func->getDeclContext()) &&
-            cast<CXXRecordDecl>(Func->getDeclContext())->isLocalClass() &&
-            CodeSynthesisContexts.size())
-          PendingLocalImplicitInstantiations.push_back(
-              std::make_pair(Func, PointOfInstantiation));
-        else if (Func->isConstexpr())
-          // Do not defer instantiations of constexpr functions, to avoid the
-          // expression evaluator needing to call back into Sema if it sees a
-          // call to such a function.
-          InstantiateFunctionDefinition(PointOfInstantiation, Func);
-        else {
-          Func->setInstantiationIsPending(true);
-          PendingInstantiations.push_back(
-              std::make_pair(Func, PointOfInstantiation));
-          // Notify the consumer that a function was implicitly instantiated.
-          Consumer.HandleCXXImplicitFunctionInstantiation(Func);
+        if (FirstInstantiation || TSK != TSK_ImplicitInstantiation ||
+            Func->isConstexpr()) {
+          if (isa<CXXRecordDecl>(Func->getDeclContext()) &&
+              cast<CXXRecordDecl>(Func->getDeclContext())->isLocalClass() &&
+              CodeSynthesisContexts.size())
+            PendingLocalImplicitInstantiations.push_back(
+                std::make_pair(Func, PointOfInstantiation));
+          else if (Func->isConstexpr())
+            // Do not defer instantiations of constexpr functions, to avoid the
+            // expression evaluator needing to call back into Sema if it sees a
+            // call to such a function.
+            InstantiateFunctionDefinition(PointOfInstantiation, Func);
+          else {
+            Func->setInstantiationIsPending(true);
+            PendingInstantiations.push_back(
+                std::make_pair(Func, PointOfInstantiation));
+            // Notify the consumer that a function was implicitly instantiated.
+            Consumer.HandleCXXImplicitFunctionInstantiation(Func);
+          }
+        }
+      } else {
+        // Walk redefinitions, as some of them may be instantiable.
+        for (auto i : Func->redecls()) {
+          if (!i->isUsed(false) && i->isImplicitlyInstantiable())
+            MarkFunctionReferenced(Loc, i, MightBeOdrUse);
         }
       }
-    } else {
-      // Walk redefinitions, as some of them may be instantiable.
-      for (auto i : Func->redecls()) {
-        if (!i->isUsed(false) && i->isImplicitlyInstantiable())
-          MarkFunctionReferenced(Loc, i, MightBeOdrUse);
-      }
-    }
+    });
   }
 
   // If this is the first "real" use, act on that.
@@ -16493,7 +16509,9 @@ static void DoMarkVarDeclReferenced(Sema &SemaRef, SourceLocation Loc,
         if (UsableInConstantExpr) {
           // Do not defer instantiations of variables that could be used in a
           // constant expression.
-          SemaRef.InstantiateVariableDefinition(PointOfInstantiation, Var);
+          SemaRef.runWithSufficientStackSpace(PointOfInstantiation, [&] {
+            SemaRef.InstantiateVariableDefinition(PointOfInstantiation, Var);
+          });
         } else if (FirstInstantiation ||
                    isa<VarTemplateSpecializationDecl>(Var)) {
           // FIXME: For a specialization of a variable template, we don't
diff --git a/lib/Sema/SemaInit.cpp b/lib/Sema/SemaInit.cpp
index 3aa38b27c5..83c475a5f1 100644
--- a/lib/Sema/SemaInit.cpp
+++ b/lib/Sema/SemaInit.cpp
@@ -6242,8 +6242,11 @@ PerformConstructorInitialization(Sema &S,
     // the definition for completely trivial constructors.
     assert(Constructor->getParent() && "No parent class for constructor.");
     if (Constructor->isDefaulted() && Constructor->isDefaultConstructor() &&
-        Constructor->isTrivial() && !Constructor->isUsed(false))
-      S.DefineImplicitDefaultConstructor(Loc, Constructor);
+        Constructor->isTrivial() && !Constructor->isUsed(false)) {
+      S.runWithSufficientStackSpace(Loc, [&] {
+        S.DefineImplicitDefaultConstructor(Loc, Constructor);
+      });
+    }
   }
 
   ExprResult CurInit((Expr *)nullptr);
diff --git a/lib/Sema/SemaLookup.cpp b/lib/Sema/SemaLookup.cpp
index 8bae219f5a..16fc822e5d 100644
--- a/lib/Sema/SemaLookup.cpp
+++ b/lib/Sema/SemaLookup.cpp
@@ -3088,8 +3088,11 @@ Sema::SpecialMemberOverloadResult Sema::LookupSpecialMember(CXXRecordDecl *RD,
   SpecialMemberCache.InsertNode(Result, InsertPoint);
 
   if (SM == CXXDestructor) {
-    if (RD->needsImplicitDestructor())
-      DeclareImplicitDestructor(RD);
+    if (RD->needsImplicitDestructor()) {
+      runWithSufficientStackSpace(RD->getLocation(), [&] {
+        DeclareImplicitDestructor(RD);
+      });
+    }
     CXXDestructorDecl *DD = RD->getDestructor();
     assert(DD && "record without a destructor");
     Result->setMethod(DD);
@@ -3112,21 +3115,36 @@ Sema::SpecialMemberOverloadResult Sema::LookupSpecialMember(CXXRecordDecl *RD,
   if (SM == CXXDefaultConstructor) {
     Name = Context.DeclarationNames.getCXXConstructorName(CanTy);
     NumArgs = 0;
-    if (RD->needsImplicitDefaultConstructor())
-      DeclareImplicitDefaultConstructor(RD);
+    if (RD->needsImplicitDefaultConstructor()) {
+      runWithSufficientStackSpace(RD->getLocation(), [&] {
+        DeclareImplicitDefaultConstructor(RD);
+      });
+    }
   } else {
     if (SM == CXXCopyConstructor || SM == CXXMoveConstructor) {
       Name = Context.DeclarationNames.getCXXConstructorName(CanTy);
-      if (RD->needsImplicitCopyConstructor())
-        DeclareImplicitCopyConstructor(RD);
-      if (getLangOpts().CPlusPlus11 && RD->needsImplicitMoveConstructor())
-        DeclareImplicitMoveConstructor(RD);
+      if (RD->needsImplicitCopyConstructor()) {
+        runWithSufficientStackSpace(RD->getLocation(), [&] {
+          DeclareImplicitCopyConstructor(RD);
+        });
+      }
+      if (getLangOpts().CPlusPlus11 && RD->needsImplicitMoveConstructor()) {
+        runWithSufficientStackSpace(RD->getLocation(), [&] {
+          DeclareImplicitMoveConstructor(RD);
+        });
+      }
     } else {
       Name = Context.DeclarationNames.getCXXOperatorName(OO_Equal);
-      if (RD->needsImplicitCopyAssignment())
-        DeclareImplicitCopyAssignment(RD);
-      if (getLangOpts().CPlusPlus11 && RD->needsImplicitMoveAssignment())
-        DeclareImplicitMoveAssignment(RD);
+      if (RD->needsImplicitCopyAssignment()) {
+        runWithSufficientStackSpace(RD->getLocation(), [&] {
+          DeclareImplicitCopyAssignment(RD);
+        });
+      }
+      if (getLangOpts().CPlusPlus11 && RD->needsImplicitMoveAssignment()) {
+        runWithSufficientStackSpace(RD->getLocation(), [&] {
+          DeclareImplicitMoveAssignment(RD);
+        });
+      }
     }
 
     if (ConstArg)
@@ -3283,12 +3301,14 @@ CXXConstructorDecl *Sema::LookupMovingConstructor(CXXRecordDecl *Class,
 DeclContext::lookup_result Sema::LookupConstructors(CXXRecordDecl *Class) {
   // If the implicit constructors have not yet been declared, do so now.
   if (CanDeclareSpecialMemberFunction(Class)) {
-    if (Class->needsImplicitDefaultConstructor())
-      DeclareImplicitDefaultConstructor(Class);
-    if (Class->needsImplicitCopyConstructor())
-      DeclareImplicitCopyConstructor(Class);
-    if (getLangOpts().CPlusPlus11 && Class->needsImplicitMoveConstructor())
-      DeclareImplicitMoveConstructor(Class);
+    runWithSufficientStackSpace(Class->getLocation(), [&] {
+      if (Class->needsImplicitDefaultConstructor())
+        DeclareImplicitDefaultConstructor(Class);
+      if (Class->needsImplicitCopyConstructor())
+        DeclareImplicitCopyConstructor(Class);
+      if (getLangOpts().CPlusPlus11 && Class->needsImplicitMoveConstructor())
+        DeclareImplicitMoveConstructor(Class);
+    });
   }
 
   CanQualType T = Context.getCanonicalType(Context.getTypeDeclType(Class));
diff --git a/lib/Sema/SemaTemplate.cpp b/lib/Sema/SemaTemplate.cpp
index d230ec90d7..00771e2246 100644
--- a/lib/Sema/SemaTemplate.cpp
+++ b/lib/Sema/SemaTemplate.cpp
@@ -20,6 +20,7 @@
 #include "clang/Basic/Builtins.h"
 #include "clang/Basic/LangOptions.h"
 #include "clang/Basic/PartialDiagnostic.h"
+#include "clang/Basic/Stack.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Sema/DeclSpec.h"
 #include "clang/Sema/Lookup.h"
diff --git a/lib/Sema/SemaTemplateDeduction.cpp b/lib/Sema/SemaTemplateDeduction.cpp
index b55a232d26..a75af62bf3 100644
--- a/lib/Sema/SemaTemplateDeduction.cpp
+++ b/lib/Sema/SemaTemplateDeduction.cpp
@@ -4632,8 +4632,11 @@ bool Sema::DeduceReturnType(FunctionDecl *FD, SourceLocation Loc,
 
       // We might need to deduce the return type by instantiating the definition
       // of the operator() function.
-      if (CallOp->getReturnType()->isUndeducedType())
-        InstantiateFunctionDefinition(Loc, CallOp);
+      if (CallOp->getReturnType()->isUndeducedType()) {
+        runWithSufficientStackSpace(Loc, [&] {
+          InstantiateFunctionDefinition(Loc, CallOp);
+        });
+      }
     }
 
     if (CallOp->isInvalidDecl())
@@ -4654,8 +4657,11 @@ bool Sema::DeduceReturnType(FunctionDecl *FD, SourceLocation Loc,
     return false;
   }
 
-  if (FD->getTemplateInstantiationPattern())
-    InstantiateFunctionDefinition(Loc, FD);
+  if (FD->getTemplateInstantiationPattern()) {
+    runWithSufficientStackSpace(Loc, [&] {
+      InstantiateFunctionDefinition(Loc, FD);
+    });
+  }
 
   bool StillUndeduced = FD->getReturnType()->isUndeducedType();
   if (StillUndeduced && Diagnose && !FD->isInvalidDecl()) {
diff --git a/lib/Sema/SemaTemplateInstantiate.cpp b/lib/Sema/SemaTemplateInstantiate.cpp
index 973f564d30..d1ecefcc0c 100644
--- a/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/lib/Sema/SemaTemplateInstantiate.cpp
@@ -19,6 +19,7 @@
 #include "clang/AST/Expr.h"
 #include "clang/AST/PrettyDeclStackTrace.h"
 #include "clang/Basic/LangOptions.h"
+#include "clang/Basic/Stack.h"
 #include "clang/Sema/DeclSpec.h"
 #include "clang/Sema/Initialization.h"
 #include "clang/Sema/Lookup.h"
@@ -365,6 +366,11 @@ void Sema::pushCodeSynthesisContext(CodeSynthesisContext Ctx) {
 
   if (!Ctx.isInstantiationRecord())
     ++NonInstantiationEntries;
+
+  // Check to see if we're low on stack space. We can't do anything about this
+  // from here, but we can at least warn the user.
+  if (isStackNearlyExhausted())
+    warnStackExhausted(Ctx.PointOfInstantiation);
 }
 
 void Sema::popCodeSynthesisContext() {
diff --git a/lib/Sema/SemaTemplateInstantiateDecl.cpp b/lib/Sema/SemaTemplateInstantiateDecl.cpp
index f340b68df6..6e4f9b9947 100644
--- a/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -3413,7 +3413,11 @@ Decl *Sema::SubstDecl(Decl *D, DeclContext *Owner,
   if (D->isInvalidDecl())
     return nullptr;
 
-  return Instantiator.Visit(D);
+  Decl *SubstD;
+  runWithSufficientStackSpace(D->getLocation(), [&] {
+    SubstD = Instantiator.Visit(D);
+  });
+  return SubstD;
 }
 
 /// Instantiates a nested template parameter list in the current
diff --git a/lib/Sema/SemaType.cpp b/lib/Sema/SemaType.cpp
index 401874edf2..4b16a09307 100644
--- a/lib/Sema/SemaType.cpp
+++ b/lib/Sema/SemaType.cpp
@@ -7729,7 +7729,9 @@ void Sema::completeExprArrayBound(Expr *E) {
         auto *Def = Var->getDefinition();
         if (!Def) {
           SourceLocation PointOfInstantiation = E->getExprLoc();
-          InstantiateVariableDefinition(PointOfInstantiation, Var);
+          runWithSufficientStackSpace(PointOfInstantiation, [&] {
+            InstantiateVariableDefinition(PointOfInstantiation, Var);
+          });
           Def = Var->getDefinition();
 
           // If we don't already have a point of instantiation, and we managed
@@ -8067,9 +8069,11 @@ bool Sema::RequireCompleteTypeImpl(SourceLocation Loc, QualType T,
     } else if (auto *ClassTemplateSpec =
             dyn_cast<ClassTemplateSpecializationDecl>(RD)) {
       if (ClassTemplateSpec->getSpecializationKind() == TSK_Undeclared) {
-        Diagnosed = InstantiateClassTemplateSpecialization(
-            Loc, ClassTemplateSpec, TSK_ImplicitInstantiation,
-            /*Complain=*/Diagnoser);
+        runWithSufficientStackSpace(Loc, [&] {
+          Diagnosed = InstantiateClassTemplateSpecialization(
+              Loc, ClassTemplateSpec, TSK_ImplicitInstantiation,
+              /*Complain=*/Diagnoser);
+        });
         Instantiated = true;
       }
     } else {
@@ -8080,10 +8084,12 @@ bool Sema::RequireCompleteTypeImpl(SourceLocation Loc, QualType T,
         // This record was instantiated from a class within a template.
         if (MSI->getTemplateSpecializationKind() !=
             TSK_ExplicitSpecialization) {
-          Diagnosed = InstantiateClass(Loc, RD, Pattern,
-                                       getTemplateInstantiationArgs(RD),
-                                       TSK_ImplicitInstantiation,
-                                       /*Complain=*/Diagnoser);
+          runWithSufficientStackSpace(Loc, [&] {
+            Diagnosed = InstantiateClass(Loc, RD, Pattern,
+                                         getTemplateInstantiationArgs(RD),
+                                         TSK_ImplicitInstantiation,
+                                         /*Complain=*/Diagnoser);
+          });
           Instantiated = true;
         }
       }