[SimplifyCFG] Merge debug locations when hoisting an instruction from a then/else branch. NFC.

[andreadb]

Summary

Now that a new API to merge debug locations has been committed at r289661 (see revision D26256 for more details), we can use it to "improve" the following commit: https://reviews.llvm.org/rL280995

Instead of nulling the debugloc of a commoned instruction, we use the "merged" debug location.
At the moment, this is just a no functional change since function getMergedLocation is just a stub and would always return a null location.

Please let me know if okay to commit.

Thanks,
Andrea

[aprantl]

Awesome, thanks!

lib/Transforms/Utils/SimplifyCFG.cpp

1279 ↗

(On Diff #81567)

Wouldn't it make more sense to make getMergedLocation() be an identity operation if the locations are identical?

[andreadb]

Thanks for the review Adrian.

lib/Transforms/Utils/SimplifyCFG.cpp

1279 ↗

(On Diff #81567)

Yes.

I was chatting with Robert about this. He told me that he plans to send a patch to improve DILocation::getMergeLocation() and fix the FIXMEs in DILocation::canDiscriminate(). From what I understand, his idea is to use DILocation::canDiscriminate() from within getMergeLocation to disambiguate cases where two locations are identical (not just same pointers, but also same values).

If it is okay for you, then I would just commit this patch and leave to Rob the task of improving getMergedLocation(). What do you think?

[aprantl]

Yes, just keep an eye on the patch and make sure that the cleanup is applied in SimplifyCFG.cpp when it is ready.

thanks!

llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp

 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/CallSite.h"
 #include "llvm/IR/CFG.h"
 #include "llvm/IR/Constant.h"
 #include "llvm/IR/ConstantRange.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
-#include "llvm/IR/DebugLoc.h"
+#include "llvm/IR/DebugInfo.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/GlobalValue.h"
 #include "llvm/IR/GlobalVariable.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/IntrinsicInst.h"
unsigned KnownIDs[] = {LLVMContext::MD_tbaa,
                            LLVMContext::MD_align,
                            LLVMContext::MD_dereferenceable,
                            LLVMContext::MD_dereferenceable_or_null,
                            LLVMContext::MD_mem_parallel_loop_access};
     combineMetadata(I1, I2, KnownIDs);
 
     // If the debug loc for I1 and I2 are different, as we are combining them
     // into one instruction, we do not want to select debug loc randomly from 
-    // I1 or I2. Instead, we set the 0-line DebugLoc to note that we do not
-    // know the debug loc of the hoisted instruction.
+    // I1 or I2.
     if (!isa<CallInst>(I1) &&  I1->getDebugLoc() != I2->getDebugLoc())
-      I1->setDebugLoc(DebugLoc());
+      I1->setDebugLoc(
+          DILocation::getMergedLocation(I1->getDebugLoc(), I2->getDebugLoc()));
  
     I2->eraseFromParent();
     Changed = true;
 
     I1 = &*BB1_Itr++;
     I2 = &*BB2_Itr++;
     // Skip debug info if it is not identical.
     DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);