[llvm] API for encoding/decoding DWARF discriminators.

Summary:
Added a pair of APIs for encoding/decoding the 3 components of a DWARF discriminator described in http://lists.llvm.org/pipermail/llvm-dev/2016-October/106532.html: the base discriminator, the duplication factor (useful in profile-guided optimization) and the copy index (used to identify copies of code in cases like loop unrolling)

The encoding packs 3 unsigned values in 32 bits. This CL addresses 2 issues:
- communicates overflow back to the user
- supports encoding all 3 components together. Current APIs assume a sequencing of events. For example, creating a new discriminator based on an existing one by changing the base discriminator was not supported.

Reviewers: davidxl, danielcdh, wmi, dblaikie

Reviewed By: dblaikie

Subscribers: zzheng, dmgreen, aprantl, JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D55681

llvm-svn: 349973

1 files changed, 9 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopUnrollAndJam.cpp b/llvm/lib/Transforms/Utils/LoopUnrollAndJam.cpp
index b5d80f6..e267626 100644
--- a/llvm/lib/Transforms/Utils/LoopUnrollAndJam.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnrollAndJam.cpp
@@ -300,8 +300,15 @@ LoopUnrollResult llvm::UnrollAndJamLoop(
     for (BasicBlock *BB : L->getBlocks())
       for (Instruction &I : *BB)
         if (!isa<DbgInfoIntrinsic>(&I))
-          if (const DILocation *DIL = I.getDebugLoc())
-            I.setDebugLoc(DIL->cloneWithDuplicationFactor(Count));
+          if (const DILocation *DIL = I.getDebugLoc()) {
+            auto NewDIL = DIL->cloneWithDuplicationFactor(Count);
+            if (NewDIL)
+              I.setDebugLoc(NewDIL.getValue());
+            else
+              LLVM_DEBUG(dbgs()
+                         << "Failed to create new discriminator: "
+                         << DIL->getFilename() << " Line: " << DIL->getLine());
+          }
 
   // Copy all blocks
   for (unsigned It = 1; It != Count; ++It) {