[MemorySSA] Expose the verify as a debug option.

[asbirlea]

Summary

Expose VerifyMemorySSA as a debug option. If set, passes will call the MSSA->verifyMemorySSA() after calling into the updater's APIs when MemorySSA should be valid.

[george.burgess.iv]

LGTM with a few comments. Thanks!

lib/Analysis/MemorySSA.cpp

80–88

Do we want to enable this by default if EXPENSIVE_CHECKS is on? Looks like the other verify* are auto-enabled (at least to some extent) in that case, and the comment above them says so.

(I'm happy in either case. I just want reasoning to point to if the answer is "we shouldn't, because ...." )

83

s/verify/verification/

[asbirlea]

Address comments.

Thank you for the review!

include/llvm/Support/Debug.h

 /// Enables verification of dominator trees.
 ///
 extern bool VerifyDomInfo;
 
 /// Enables verification of loop info.
 ///
 extern bool VerifyLoopInfo;
 
+/// Enables verification of MemorySSA.
+///
+extern bool VerifyMemorySSA;
+
 ///\}
 
 /// EnableDebugBuffering - This defaults to false.  If true, the debug
 /// stream will install signal handlers to dump any buffered debug
 /// output.  It allows clients to selectively allow the debug stream
 /// to install signal handlers if they are certain there will be no
 /// conflict.
 ///

lib/Analysis/MemorySSA.cpp

 INITIALIZE_PASS_END(MemorySSAPrinterLegacyPass, "print-memoryssa",
                     "Memory SSA Printer", false, false)
 
 static cl::opt<unsigned> MaxCheckLimit(
     "memssa-check-limit", cl::Hidden, cl::init(100),
     cl::desc("The maximum number of stores/phis MemorySSA"
              "will consider trying to walk past (default = 100)"));
 
-static cl::opt<bool>
-    VerifyMemorySSA("verify-memoryssa", cl::init(false), cl::Hidden,
-                    cl::desc("Verify MemorySSA in legacy printer pass."));
+// Always verify MemorySSA if expensive checking is enabled.
+#ifdef EXPENSIVE_CHECKS
+bool llvm::VerifyMemorySSA = true;
+#else
+bool llvm::VerifyMemorySSA = false;
+#endif
+static cl::opt<bool, true>
+    VerifyMemorySSAX("verify-memoryssa", cl::location(VerifyMemorySSA),
+                     cl::Hidden, cl::desc("Enable verification of MemorySSA."));
 
 namespace llvm {
 
 /// An assembly annotator class to print Memory SSA information in
 /// comments.
 class MemorySSAAnnotatedWriter : public AssemblyAnnotationWriter {
   friend class MemorySSA;