r359960 - Reduce amount of work ODR hashing does.

[Richard Trieu via cfe-commits]

Author: rtrieu
Date: Fri May  3 21:22:33 2019
New Revision: 359960

URL: http://llvm.org/viewvc/llvm-project?rev=359960&view=rev
Log:
Reduce amount of work ODR hashing does.

When a FunctionProtoType is in the original type in a DecayedType, the decayed
type is a PointerType which points back the original FunctionProtoType.  The
visitor for ODRHashing will attempt to process both Type's, doing double work.
By chaining together multiple DecayedType's and FunctionProtoType's, this would
result in 2^N Type's visited only N DecayedType's and N FunctionProtoType's
exsit.  Another bug where VisitDecayedType and VisitAdjustedType did
redundant work doubled the work at each level, giving 4^N Type's visited.  This
patch removed the double work and detects when a FunctionProtoType decays to
itself to only check the Type once.  This lowers the exponential runtime to
linear runtime.  Fixes https://bugs.llvm.org/show_bug.cgi?id=41625

Modified:
    cfe/trunk/lib/AST/ODRHash.cpp
    cfe/trunk/test/Modules/odr_hash.cpp

Modified: cfe/trunk/lib/AST/ODRHash.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/ODRHash.cpp?rev=359960&r1=359959&r2=359960&view=diff
==============================================================================
--- cfe/trunk/lib/AST/ODRHash.cpp (original)
+++ cfe/trunk/lib/AST/ODRHash.cpp Fri May  3 21:22:33 2019
@@ -703,14 +703,36 @@ public:
   void VisitType(const Type *T) {}
 
   void VisitAdjustedType(const AdjustedType *T) {
-    AddQualType(T->getOriginalType());
-    AddQualType(T->getAdjustedType());
+    QualType Original = T->getOriginalType();
+    QualType Adjusted = T->getAdjustedType();
+
+    // The original type and pointee type can be the same, as in the case of
+    // function pointers decaying to themselves.  Set a bool and only process
+    // the type once, to prevent doubling the work.
+    SplitQualType split = Adjusted.split();
+    if (auto Pointer = dyn_cast<PointerType>(split.Ty)) {
+      if (Pointer->getPointeeType() == Original) {
+        Hash.AddBoolean(true);
+        ID.AddInteger(split.Quals.getAsOpaqueValue());
+        AddQualType(Original);
+        VisitType(T);
+        return;
+      }
+    }
+
+    // The original type and pointee type are different, such as in the case
+    // of a array decaying to an element pointer.  Set a bool to false and
+    // process both types.
+    Hash.AddBoolean(false);
+    AddQualType(Original);
+    AddQualType(Adjusted);
+
     VisitType(T);
   }
 
   void VisitDecayedType(const DecayedType *T) {
-    AddQualType(T->getDecayedType());
-    AddQualType(T->getPointeeType());
+    // getDecayedType and getPointeeType are derived from getAdjustedType
+    // and don't need to be separately processed.
     VisitAdjustedType(T);
   }
 

Modified: cfe/trunk/test/Modules/odr_hash.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Modules/odr_hash.cpp?rev=359960&r1=359959&r2=359960&view=diff
==============================================================================
--- cfe/trunk/test/Modules/odr_hash.cpp (original)
+++ cfe/trunk/test/Modules/odr_hash.cpp Fri May  3 21:22:33 2019
@@ -4587,6 +4587,43 @@ int num = bar();
 #endif
 }
 
+namespace FunctionProtoTypeDecay {
+#if defined(FIRST)
+struct S1 {
+  struct X {};
+  using Y = X(X());
+};
+#elif defined(SECOND)
+struct S1 {
+  struct X {};
+  using Y = X(X(X()));
+};
+#else
+S1 s1;
+// expected-error at first.h:* {{'FunctionProtoTypeDecay::S1::Y' from module 'FirstModule' is not present in definition of 'FunctionProtoTypeDecay::S1' in module 'SecondModule'}}
+// expected-note at second.h:* {{declaration of 'Y' does not match}}
+#endif
+
+#if defined(FIRST)
+struct S2 {
+  struct X {};
+  using Y =
+      X(X(X(X(X(X(X(X(X(X(X(X(X(X(X(X(
+      X(X(X(X(X(X(X(X(X(X(X(X(X(X(X(X(
+      X(X(X(X(X(X(X(X(X(X(X(X(X(X(X(X(
+      X(X(X(X(X(X(X(X(X(X(X(X(X(X(X(X(
+      ))))))))))))))))
+      ))))))))))))))))
+      ))))))))))))))))
+      ))))))))))))))));
+};
+#elif defined(SECOND)
+#else
+S2 s2;
+#endif
+
+}
+
 // Keep macros contained to one file.
 #ifdef FIRST
 #undef FIRST