Allow diagnostic handlers to check for optimization remarks.

[dnovillo]

Summary

When optimization remarks are enabled via the driver flag -Rpass, we
should allow the FE diagnostic handler to check if the given pass name
needs a diagnostic.

We were unconditionally checking the pattern defined in opt's
-pass-remarks flag. This was causing the FE to not emit any diagnostics.

[qcolombet]

Hi Diego,

I'd like we take another direction for this patch. See my inline comment.

Thanks,
-Quentin

lib/IR/LLVMContext.cpp

169

I am not a huge fan of duplicating this test (i.e., this is the test used in LLVMContext::diagnose).

Could we instead teach optimizationRemarksEnabledFor to always returns true when we set a diagnostic handler?

For instance, we could change the method used to check the optimization remarks within LLVMContext::setDiagnosticHandler.

[dnovillo]

lib/IR/LLVMContext.cpp

169

Oh, sure. I had initially done that, but it didn't seem like the predicate optimizationRemarksEnabledFor() was semantically equivalent if it also checks for a handler.

I'll sink the decision in LLVMContext::setDiagnosticHandler.

[dnovillo]

I did something slightly different. Setting a new function pointer
just for the optimization remarks seemed like overkill. I am doing
something similar to what is done in the front end.

The backend handler checks whether it's dealing with an optimization
remark. If so, it further checks the regexp passed in -pass-remarks.
This seemed less invasive than the additional function pointer.

[qcolombet]

Hi Diego,

That’s a good idea.

LGTM.

Thanks,
-Quentin

lib/IR/LLVMContext.cpp

 void LLVMContext::emitError(unsigned LocCookie, const Twine &ErrorStr) {
   diagnose(DiagnosticInfoInlineAsm(LocCookie, ErrorStr));
 }
 
 void LLVMContext::emitOptimizationRemark(const char *PassName,
                                          const Function &Fn,
                                          const DebugLoc &DLoc,
                                          const Twine &Msg) {
-  if (pImpl->optimizationRemarksEnabledFor(PassName))
+  // Optimization remark diagnostics can be enabled via -Rpass= from
+  // the front end or -pass-remarks= from opt. If there is a
+  // diagnostic handler installed, we defer to it to check whether a
+  // diagnostic should be generated for \p PassName. Otherwise, call
+  // LLVMContextImpl::optimizationRemarksEnabledFor to check the
+  // pattern passed in -pass-remarks.
+  if (pImpl->DiagnosticHandler ||
+      pImpl->optimizationRemarksEnabledFor(PassName))
     diagnose(DiagnosticInfoOptimizationRemark(PassName, Fn, DLoc, Msg));
 }
 
 //===----------------------------------------------------------------------===//
 // Metadata Kind Uniquing
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 #ifndef NDEBUG