Fix nullptr access

[vivekvpandya]

Summary

[GlobalISel]
Do not pass nullptr in MachineOptimizationRemark constructor, as MBB pointer is used in DiagnosticInfoMIROptimization constructor and that results in nullptr access.

[arsenm]

Testcase? Also typo in message

[vivekvpandya]

In D75018#1889213, @arsenm wrote:

Testcase? Also typo in message

I discovered this while creating basic blocks in custom instruction selection for a downstream back-end. I don't know how to write that scenario in a test.

[arsenm]

Is this still an issue? This is still null

[arsenm]

Pointing at the entry block is probably not useful, probably should just go with the function for the report

llvm/lib/CodeGen/GlobalISel/InstructionSelect.cpp

if (Ty.isValid() && Ty.getSizeInBits() > TRI.getRegSizeInBits(*RC)) {
           "VReg's low-level type and register class have different sizes", *MI);
       return false;
     }
   }
 
   if (MF.size() != NumBlocks) {
     MachineOptimizationRemarkMissed R("gisel-select", "GISelFailure",
                                       MF.getFunction().getSubprogram(),
-                                      /*MBB=*/nullptr);
+                                      &MF.front());
     R << "inserting blocks is not supported yet";
     reportGISelFailure(MF, TPC, MORE, R);
     return false;
   }
 #endif
   auto &TLI = *MF.getSubtarget().getTargetLowering();
   TLI.finalizeLowering(MF);
 

llvm/lib/CodeGen/GlobalISel/Legalizer.cpp

reportGISelFailure(MF, TPC, MORE, "gisel-legalize",
                        "unable to legalize instruction", *Result.FailedOn);
     return false;
   }
   // For now don't support if new blocks are inserted - we would need to fix the
   // outer loop for that.
   if (MF.size() != NumBlocks) {
     MachineOptimizationRemarkMissed R("gisel-legalize", "GISelFailure",
                                       MF.getFunction().getSubprogram(),
-                                      /*MBB=*/nullptr);
+                                      &MF.front());
     R << "inserting blocks is not supported yet";
     reportGISelFailure(MF, TPC, MORE, R);
     return false;
   }
   // If for some reason CSE was not enabled, make sure that we invalidate the
   // CSEInfo object (as we currently declare that the analysis is preserved).
   // The next time get on the wrapper is called, it will force it to recompute
   // the analysis.
   if (!EnableCSE)
     Wrapper.setComputed(false);
   return Result.Changed;
 }