commit 87a3180343481a051ca3130969cfbceb41aee96f
author Reid Kleckner <rnk@google.com> Mon Mar 12 21:43:02 2018 +0000
committer Reid Kleckner <rnk@google.com> Mon Mar 12 21:43:02 2018 +0000
tree e352bfc508e21e647fb94234ec2b07c0dbc8a9c4
parent 7147f32ec52939f70d54d977a38cedb78c6b94af

Re-land "[Sema] Make getCurFunction() return null outside function parsing"

This relands r326965.

There was a null dereference in typo correction that was triggered in
Sema/diagnose_if.c. We are not always in a function scope when doing
typo correction. The fix is to add a null check.

LLVM's optimizer made it hard to find this bug. I wrote it up in a
not-very-well-editted blog post here:
http://qinsb.blogspot.com/2018/03/ub-will-delete-your-null-checks.html

llvm-svn: 327334

clang/lib/Sema/SemaExprCXX.cpp

diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index d3ab003..4baf52f 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -1114,8 +1114,9 @@
 
   assert((!ByCopy || Explicit) && "cannot implicitly capture *this by value");
 
-  const unsigned MaxFunctionScopesIndex = FunctionScopeIndexToStopAt ?
-    *FunctionScopeIndexToStopAt : FunctionScopes.size() - 1;
+  const int MaxFunctionScopesIndex = FunctionScopeIndexToStopAt
+                                         ? *FunctionScopeIndexToStopAt
+                                         : FunctionScopes.size() - 1;
 
   // Check that we can capture the *enclosing object* (referred to by '*this')
   // by the capturing-entity/closure (lambda/block/etc) at
@@ -1141,7 +1142,7 @@
 
 
   unsigned NumCapturingClosures = 0;
-  for (unsigned idx = MaxFunctionScopesIndex; idx != 0; idx--) {
+  for (int idx = MaxFunctionScopesIndex; idx >= 0; idx--) {
     if (CapturingScopeInfo *CSI =
             dyn_cast<CapturingScopeInfo>(FunctionScopes[idx])) {
       if (CSI->CXXThisCaptureIndex != 0) {
@@ -1196,8 +1197,8 @@
   // FIXME: We need to delay this marking in PotentiallyPotentiallyEvaluated
   // contexts.
   QualType ThisTy = getCurrentThisType();
-  for (unsigned idx = MaxFunctionScopesIndex; NumCapturingClosures;
-      --idx, --NumCapturingClosures) {
+  for (int idx = MaxFunctionScopesIndex; NumCapturingClosures;
+       --idx, --NumCapturingClosures) {
     CapturingScopeInfo *CSI = cast<CapturingScopeInfo>(FunctionScopes[idx]);
     Expr *ThisExpr = nullptr;
 
@@ -7176,9 +7177,6 @@
 
   const bool IsFullExprInstantiationDependent = FE->isInstantiationDependent();
 
-  ArrayRef<const FunctionScopeInfo *> FunctionScopesArrayRef(
-      S.FunctionScopes.data(), S.FunctionScopes.size());
-
   // All the potentially captureable variables in the current nested
   // lambda (within a generic outer lambda), must be captured by an
   // outer lambda that is enclosed within a non-dependent context.
@@ -7207,7 +7205,7 @@
     // capture the variable in that lambda (and all its enclosing lambdas).
     if (const Optional<unsigned> Index =
             getStackIndexOfNearestEnclosingCaptureCapableLambda(
-                FunctionScopesArrayRef, Var, S)) {
+                S.FunctionScopes, Var, S)) {
       const unsigned FunctionScopeIndexOfCapturableLambda = Index.getValue();
       MarkVarDeclODRUsed(Var, VarExpr->getExprLoc(), S,
                          &FunctionScopeIndexOfCapturableLambda);
@@ -7243,7 +7241,7 @@
     // 'this' in that lambda (and all its enclosing lambdas).
     if (const Optional<unsigned> Index =
             getStackIndexOfNearestEnclosingCaptureCapableLambda(
-                FunctionScopesArrayRef, /*0 is 'this'*/ nullptr, S)) {
+                S.FunctionScopes, /*0 is 'this'*/ nullptr, S)) {
       const unsigned FunctionScopeIndexOfCapturableLambda = Index.getValue();
       S.CheckCXXThisCapture(CurrentLSI->PotentialThisCaptureLocation,
                             /*Explicit*/ false, /*BuildAndDiagnose*/ true,