Revert "[clang] Add early exit when checking for const init of arrays."

[adamcz]

Summary

This reverts commit 48bb5f4cbe8d5951c1153e469dc6713a122b7fa3.

Several breakages, including ARM (fixed later, but not sufficient) and
MSan (to be diagnosed later).

clang/lib/AST/ExprConstant.cpp

 
 bool ArrayExprEvaluator::VisitCXXConstructExpr(const CXXConstructExpr *E,
                                                const LValue &Subobject,
                                                APValue *Value,
                                                QualType Type) {
   bool HadZeroInit = Value->hasValue();
 
   if (const ConstantArrayType *CAT = Info.Ctx.getAsConstantArrayType(Type)) {
-    unsigned FinalSize = CAT->getSize().getZExtValue();
+    unsigned N = CAT->getSize().getZExtValue();
 
     // Preserve the array filler if we had prior zero-initialization.
     APValue Filler =
       HadZeroInit && Value->hasArrayFiller() ? Value->getArrayFiller()
                                              : APValue();
 
-    *Value = APValue(APValue::UninitArray(), 0, FinalSize);
-    if (FinalSize == 0)
-      return true;
-
-    LValue ArrayElt = Subobject;
-    ArrayElt.addArray(Info, E, CAT);
-    // We do the whole initialization in two passes, first for just one element,
-    // then for the whole array. It's possible we may find out we can't do const
-    // init in the first pass, in which case we avoid allocating a potentially
-    // large array. We don't do more passes because expanding array requires
-    // copying the data, which is wasteful.
-    for (const unsigned N : {1u, FinalSize}) {
-      unsigned OldElts = Value->getArrayInitializedElts();
-      if (OldElts == N)
-        break;
-
-      // Expand the array to appropriate size.
-      APValue NewValue(APValue::UninitArray(), N, FinalSize);
-      for (unsigned I = 0; I < OldElts; ++I)
-        NewValue.getArrayInitializedElt(I).swap(
-            Value->getArrayInitializedElt(I));
-      Value->swap(NewValue);
+    *Value = APValue(APValue::UninitArray(), N, N);
 
-      if (HadZeroInit)
-        for (unsigned I = OldElts; I < N; ++I)
-          Value->getArrayInitializedElt(I) = Filler;
+      for (unsigned I = 0; I != N; ++I)
 
-      // Initialize the elements.
-      for (unsigned I = OldElts; I < N; ++I) {
-        if (!VisitCXXConstructExpr(E, ArrayElt,
-                                   &Value->getArrayInitializedElt(I),
-                                   CAT->getElementType()) ||
-            !HandleLValueArrayAdjustment(Info, E, ArrayElt,
-                                         CAT->getElementType(), 1))
-          return false;
-        // When checking for const initilization any diagnostic is considered
-        // an error.
-        if (Info.EvalStatus.Diag && !Info.EvalStatus.Diag->empty() &&
-            !Info.keepEvaluatingAfterFailure())
-          return false;
-      }
-    }
+    LValue ArrayElt = Subobject;
+    ArrayElt.addArray(Info, E, CAT);
+    for (unsigned I = 0; I != N; ++I)
+      if (!VisitCXXConstructExpr(E, ArrayElt, &Value->getArrayInitializedElt(I),
+          !HandleLValueArrayAdjustment(Info, E, ArrayElt, CAT->getElementType(),
+                                       1))
 
     return true;
   }
 
   if (!Type->isRecordType())
     return Error(E);
 
   return RecordExprEvaluator(Info, Subobject, *Value)

clang/test/SemaCXX/PR51712-large-array-constexpr-check-oom.cpp

-// REQUIRES: shell
-// UNSUPPORTED: win32
-// RUN: ulimit -v 1048576
-// RUN: %clang_cc1 -std=c++11 -fsyntax-only -verify -triple=x86_64 %s
-// expected-no-diagnostics
-
-// This used to require too much memory and crash with OOM.
-struct {
-  int a, b, c, d;
-} arr[1<<30];
-