[sil] Add a SILVerifier check that all SILUndef's parent function back pointer contains the SILFunction that maps to it.

Author: gottesmm

include/swift/SIL/SILFunction.h

@@ -332,7 +332,11 @@ class SILFunction
   PerformanceConstraints perfConstraints = PerformanceConstraints::None;
 
   /// This is the set of undef values we've created, for uniquing purposes.
-  llvm::DenseMap<SILType, SILUndef *> undefValues;
+  ///
+  /// We use a SmallDenseMap since in most functions, we will have only one type
+  /// of undef if we have any at all. In that case, by staying small we avoid
+  /// needing a heap allocation.
+  llvm::SmallDenseMap<SILType, SILUndef *, 1> undefValues;
 
   /// This is the number of uses of this SILFunction inside the SIL.
   /// It does not include references from debug scopes.
@@ -1563,6 +1567,12 @@ class SILFunction
   /// This is a fast subset of the checks performed in the SILVerifier.
   void verifyCriticalEdges() const;
 
+  /// Validate that all SILUndefs stored in the function's type -> SILUndef map
+  /// have this function as their parent function.
+  ///
+  /// Please only call this from the SILVerifier.
+  void verifySILUndefMap() const;
+
   /// Pretty-print the SILFunction.
   void dump(bool Verbose) const;
   void dump() const;

lib/SIL/Verifier/SILVerifier.cpp

@@ -6902,6 +6902,11 @@ class SILVerifier : public SILVerifierBase<SILVerifier> {
               "generic function definition must have a generic environment");
     }
 
+    // Before verifying the body of the function, validate the SILUndef map to
+    // make sure that all SILUndef in the function's map point at the function
+    // as the SILUndef's parent.
+    F->verifySILUndefMap();
+
     // Otherwise, verify the body of the function.
     verifyEntryBlock(F->getEntryBlock());
     verifyEpilogBlocks(F);
@@ -6974,6 +6979,15 @@ void SILFunction::verifyCriticalEdges() const {
                      /*checkLinearLifetime=*/ false).verifyBranches(this);
 }
 
+/// Validate that all SILUndef in \p f have f as a parent.
+void SILFunction::verifySILUndefMap() const {
+  for (auto &pair : undefValues) {
+    assert(
+        pair.second->getParent() == this &&
+        "undef in f->undefValue map with different parent function than f?!");
+  }
+}
+
 /// Verify that a property descriptor follows invariants.
 void SILProperty::verify(const SILModule &M) const {
   if (!verificationEnabled(M))