[Profile] deprecate __llvm_profile_override_default_filename (part-1)

[davidxl]

Summary

When non-default profile name is specified on command line, the current instrumentation needs to synthesize llvm_profile_init function and emits function call to llvm_profile_override_filename (in addition to creating a char array variable with private linkage to hold the name).

In fact, such calls are completely unnecessary. It is enough to promote the profile name var to global linkage in comdat (or weakany) and eliminate the call. The text size will be reduced, so will the readonly data size (duplicates gets commoned). The runtime start up time will also improve slightly.

[vsk]

Nice, just one concern.

lib/Transforms/Instrumentation/InstrProfiling.cpp

615

What's the advantage of placing the file name var in a comdat if it already has weak linkage? Would some ELF tests break without this?

[vsk]

LGTM.

include/llvm/ProfileData/InstrProfData.inc

  * bits (i.e. bit 56) to 1 to indicate if this is an IR-level instrumentaiton
  * generated profile, and 0 if this is a Clang FE generated profile.
  */
 #define VARIANT_MASKS_ALL 0xff00000000000000ULL
 #define GET_VERSION(V) ((V) & ~VARIANT_MASKS_ALL)
 #define VARIANT_MASK_IR_PROF (0x1ULL << 56)
 #define IR_LEVEL_PROF_VERSION_VAR __llvm_profile_raw_version
 
+/* The variable that holds the name of the profile data
+ * specified via command line. */
+#define INSTR_PROF_PROFILE_NAME_VAR __llvm_profile_filename
+
 /* Runtime section names and name strings.  */
 #define INSTR_PROF_DATA_SECT_NAME __llvm_prf_data
 #define INSTR_PROF_NAME_SECT_NAME __llvm_prf_names
 #define INSTR_PROF_CNTS_SECT_NAME __llvm_prf_cnts
 /* Array of pointers. Each pointer points to a list
  * of value nodes associated with one value site.
  */
 #define INSTR_PROF_VALS_SECT_NAME __llvm_prf_vals

lib/Transforms/Instrumentation/InstrProfiling.cpp

LLVMUsed =
       new GlobalVariable(*M, ATy, false, GlobalValue::AppendingLinkage,
                          ConstantArray::get(ATy, MergedVars), "llvm.used");
   LLVMUsed->setSection("llvm.metadata");
 }
 
 void InstrProfiling::emitInitialization() {
   std::string InstrProfileOutput = Options.InstrProfileOutput;
 
+  if (!InstrProfileOutput.empty()) {
+    // Create variable for profile name.
+    Constant *ProfileNameConst =
+        ConstantDataArray::getString(M->getContext(), InstrProfileOutput, true);
+    GlobalVariable *ProfileNameVar = new GlobalVariable(
+        *M, ProfileNameConst->getType(), true, GlobalValue::WeakAnyLinkage,
+        ProfileNameConst, INSTR_PROF_QUOTE(INSTR_PROF_PROFILE_NAME_VAR));
+    Triple TT(M->getTargetTriple());
+    if (TT.supportsCOMDAT())
+      ProfileNameVar->setComdat(M->getOrInsertComdat(
+          StringRef(INSTR_PROF_QUOTE(INSTR_PROF_PROFILE_NAME_VAR))));
+  }
+
   Constant *RegisterF = M->getFunction(getInstrProfRegFuncsName());
-  if (!RegisterF && InstrProfileOutput.empty())
+  if (!RegisterF)
     return;
 
   // Create the initialization function.
   auto *VoidTy = Type::getVoidTy(M->getContext());
   auto *F = Function::Create(FunctionType::get(VoidTy, false),
                              GlobalValue::InternalLinkage,
                              getInstrProfInitFuncName(), M);
   F->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);
   F->addFnAttr(Attribute::NoInline);
   if (Options.NoRedZone)
     F->addFnAttr(Attribute::NoRedZone);
 
   // Add the basic block and the necessary calls.
   IRBuilder<> IRB(BasicBlock::Create(M->getContext(), "", F));
   if (RegisterF)
     IRB.CreateCall(RegisterF, {});
-  if (!InstrProfileOutput.empty()) {
-    auto *Int8PtrTy = Type::getInt8PtrTy(M->getContext());
-    auto *SetNameTy = FunctionType::get(VoidTy, Int8PtrTy, false);
-    auto *SetNameF = Function::Create(SetNameTy, GlobalValue::ExternalLinkage,
-                                      getInstrProfFileOverriderFuncName(), M);
-
-    // Create variable for profile name.
-    Constant *ProfileNameConst =
-        ConstantDataArray::getString(M->getContext(), InstrProfileOutput, true);
-    GlobalVariable *ProfileName =
-        new GlobalVariable(*M, ProfileNameConst->getType(), true,
-                           GlobalValue::PrivateLinkage, ProfileNameConst);
-
-    IRB.CreateCall(SetNameF, IRB.CreatePointerCast(ProfileName, Int8PtrTy));
-  }
   IRB.CreateRetVoid();
 
   appendToGlobalCtors(*M, F, 0);
 }