[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, 23 insertions, 6 deletions

diff --git a/llvm/lib/Transforms/Utils/AddDiscriminators.cpp b/llvm/lib/Transforms/Utils/AddDiscriminators.cpp
index e3ef4236222..1e0fd5588ca 100644
--- a/llvm/lib/Transforms/Utils/AddDiscriminators.cpp
+++ b/llvm/lib/Transforms/Utils/AddDiscriminators.cpp
@@ -209,10 +209,18 @@ static bool addDiscriminators(Function &F) {
       // Only the lowest 7 bits are used to represent a discriminator to fit
       // it in 1 byte ULEB128 representation.
       unsigned Discriminator = R.second ? ++LDM[L] : LDM[L];
-      I.setDebugLoc(DIL->setBaseDiscriminator(Discriminator));
-      LLVM_DEBUG(dbgs() << DIL->getFilename() << ":" << DIL->getLine() << ":"
-                        << DIL->getColumn() << ":" << Discriminator << " " << I
-                        << "\n");
+      auto NewDIL = DIL->setBaseDiscriminator(Discriminator);
+      if (!NewDIL) {
+        LLVM_DEBUG(dbgs() << "Could not encode discriminator: "
+                          << DIL->getFilename() << ":" << DIL->getLine() << ":"
+                          << DIL->getColumn() << ":" << Discriminator << " "
+                          << I << "\n");
+      } else {
+        I.setDebugLoc(NewDIL.getValue());
+        LLVM_DEBUG(dbgs() << DIL->getFilename() << ":" << DIL->getLine() << ":"
+                   << DIL->getColumn() << ":" << Discriminator << " " << I
+                   << "\n");
+      }
       Changed = true;
     }
   }
@@ -239,8 +247,17 @@ static bool addDiscriminators(Function &F) {
           std::make_pair(CurrentDIL->getFilename(), CurrentDIL->getLine());
       if (!CallLocations.insert(L).second) {
         unsigned Discriminator = ++LDM[L];
-        Current->setDebugLoc(CurrentDIL->setBaseDiscriminator(Discriminator));
-        Changed = true;
+        auto NewDIL = CurrentDIL->setBaseDiscriminator(Discriminator);
+        if (!NewDIL) {
+          LLVM_DEBUG(dbgs()
+                     << "Could not encode discriminator: "
+                     << CurrentDIL->getFilename() << ":"
+                     << CurrentDIL->getLine() << ":" << CurrentDIL->getColumn()
+                     << ":" << Discriminator << " " << I << "\n");
+        } else {
+          Current->setDebugLoc(NewDIL.getValue());
+          Changed = true;
+        }
       }
     }
   }