[PATCH] D15852: [PGO]: Simplify coverage data lowering code

[David Li via llvm-commits]

davidxl created this revision.
davidxl added a reviewer: vsk.
davidxl added a subscriber: llvm-commits.

The names referenced by the coverage data may be associated with functions that are never emitted by Clang. That means those PGO names won't be materialized into the __llvm_prf_names section during instr-prof lowering. To make sure those names are emitted, the lowering pass will need to go through the coverage map global variable and check the referenced names.

The lowering code makes assumption about the layout of the coverage map and function record data which is error prone. Besides, in the near future, when name compression is implemented, the name references won't be available from the coverage data anymore.

In this patch, the referenced names are explicitly recorded in an internal global var and passed to the middle end. This simplifies the lowering code and also make it possible to do name compression. This is part-1 of the patch. Part-2 is in clang.

http://reviews.llvm.org/D15852

Files:
  include/llvm/ProfileData/InstrProf.h
  lib/Transforms/Instrumentation/InstrProfiling.cpp

Index: lib/Transforms/Instrumentation/InstrProfiling.cpp
===================================================================
--- lib/Transforms/Instrumentation/InstrProfiling.cpp
+++ lib/Transforms/Instrumentation/InstrProfiling.cpp
@@ -93,8 +93,8 @@
   /// Replace instrprof_increment with an increment of the appropriate value.
   void lowerIncrement(InstrProfIncrementInst *Inc);
 
-  /// Set up the section and uses for coverage data and its references.
-  void lowerCoverageData(GlobalVariable *CoverageData);
+  /// Set up name references from coverage data.
+  void lowerCoverageData(GlobalVariable *CoverageNamesVar);
 
   /// Get the region counters for an increment, creating them if necessary.
   ///
@@ -156,9 +156,9 @@
         }
       }
 
-  if (GlobalVariable *Coverage =
-          M.getNamedGlobal(getCoverageMappingVarName())) {
-    lowerCoverageData(Coverage);
+  if (GlobalVariable *CoverageNamesVar =
+          M.getNamedGlobal(getCoverageNamesVarName())) {
+    lowerCoverageData(CoverageNamesVar);
     MadeChange = true;
   }
 
@@ -233,19 +233,13 @@
   Inc->eraseFromParent();
 }
 
-void InstrProfiling::lowerCoverageData(GlobalVariable *CoverageData) {
-
-  Constant *Init = CoverageData->getInitializer();
-  // We're expecting { [4 x 32], [n x { i8*, i32, i32 }], [m x i8] }
-  // for some C. If not, the frontend's given us something broken.
-  assert(Init->getNumOperands() == 3 && "bad number of fields in coverage map");
-  assert(isa<ConstantArray>(Init->getAggregateElement(1)) &&
-         "invalid function list in coverage map");
-  ConstantArray *Records = cast<ConstantArray>(Init->getAggregateElement(1));
-  for (unsigned I = 0, E = Records->getNumOperands(); I < E; ++I) {
-    Constant *Record = Records->getOperand(I);
-    Value *V = const_cast<Value *>(Record->getOperand(0))->stripPointerCasts();
+void InstrProfiling::lowerCoverageData(GlobalVariable *CoverageNamesVar) {
 
+  ConstantArray *Names =
+      cast<ConstantArray>(CoverageNamesVar->getInitializer());
+  for (unsigned I = 0, E = Names->getNumOperands(); I < E; ++I) {
+    Constant *NC = Names->getOperand(I);
+    Value *V = NC->stripPointerCasts();
     assert(isa<GlobalVariable>(V) && "Missing reference to function name");
     GlobalVariable *Name = cast<GlobalVariable>(V);
 
Index: include/llvm/ProfileData/InstrProf.h
===================================================================
--- include/llvm/ProfileData/InstrProf.h
+++ include/llvm/ProfileData/InstrProf.h
@@ -89,6 +89,10 @@
   return "__llvm_coverage_mapping";
 }
 
+/// Return the name of the internal variable recording the array
+/// of pgo function name vars referenced by the coverage mapping.
+inline StringRef getCoverageNamesVarName() { return "__llvm_coverage_names"; }
+
 /// Return the name of function that registers all the per-function control
 /// data at program startup time by calling __llvm_register_function. This
 /// function has internal linkage and is called by  __llvm_profile_init


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D15852.43866.patch
Type: text/x-patch
Size: 2992 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20160103/0b490d9c/attachment.bin>