RequirementMachine: Verify protocol requirement signatures even in noassert builds

Author: slavapestov

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -2690,12 +2690,20 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
       llvm::errs() << "\n";
     }
 
-
-#ifndef NDEBUG
-    // In asserts builds, also verify some invariants of the requirement
-    // signature.
-    PD->getGenericSignature().verify(reqSig);
-#endif
+    if (getASTContext().LangOpts.RequirementMachineProtocolSignatures ==
+        RequirementMachineMode::Disabled) {
+  #ifndef NDEBUG
+      // The GenericSignatureBuilder outputs incorrectly-minimized signatures
+      // sometimes, so only check invariants in asserts builds.
+      PD->getGenericSignature().verify(reqSig);
+  #endif
+    } else {
+      // When using the Requirement Machine, always verify signatures.
+      // An incorrect signature indicates a serious problem which can cause
+      // miscompiles or inadvertent ABI dependencies on compiler bugs, so
+      // we really want to avoid letting one slip by.
+      PD->getGenericSignature().verify(reqSig);
+    }
 
     (void) reqSig;