Enable machine code verification with EXPENSIVE_CHECKS.

[fhahn]

Summary

Currently quite a few tests fail with this patch. I've added a ticket to track the failures: https://bugs.llvm.org/show_bug.cgi?id=32146 . We may want to hold of enabling -verify-machineinstr until all the failures are resolved.

[MatzeB]

Maybe we can add some sort of blacklisting mechanism, because it will require a lot of work to get all the targets fixed?

[fhahn]

Are you thinking about something like XFAIL-EXPENSIVE?

[RKSimon]

If at all possible I'd prefer to get some triage done on a majority of the bugs first before avoiding the problem in this way - my concern is that XFAIL tagging will be used just to ignore lurking problems that will bite back later on.

@qcolombet 's analyses in PR27481 covers quite a few cases and I think similar fixes should cover many of the remaining x86 failures, and I wouldn't be surprised if other targets are very similar.

[MatzeB]

In D30625#707389, @fhahn wrote:

Are you thinking about something like XFAIL-EXPENSIVE?

Well intuitively I would expect this to be a bigger issue, mostly because you have to get target maintainers on board to fix their targets.
Because of that I was thinking more in the lines of adding a bool TargetSubtargetInfo::isMachineVerifierClean() and adding a return false implementation to all the broken targets. That way we could fix the targets one by one.

[MatzeB]

I just proposed a "pragmatic" version of this: https://reviews.llvm.org/D33696

[fhahn]

I think we should go with @MatzeB 's patch https://reviews.llvm.org/D33696

lib/CodeGen/TargetPassConfig.cpp

 }
 
 void TargetPassConfig::addPrintPass(const std::string &Banner) {
   if (TM->shouldPrintMachineCode())
     PM->add(createMachineFunctionPrinterPass(dbgs(), Banner));
 }
 
 void TargetPassConfig::addVerifyPass(const std::string &Banner) {
+#ifndef EXPENSIVE_CHECKS
   if (VerifyMachineCode)
+#endif
     PM->add(createMachineVerifierPass(Banner));
 }
 
 /// Add common target configurable passes that perform LLVM IR to IR transforms
 /// following machine independent optimization.
 void TargetPassConfig::addIRPasses() {
   switch (UseCFLAA) {
   case CFLAAType::Steensgaard: