[PGO] Generate __llvm_profile_raw_version only when instrumentedusers/psamolysov/pgo-generate-version-when-instrumented

Currently, only modules that contain at least a single function
definition are instrumented. When a module contains no function
definitions at all, the module is not instrumented (yet?) and there is
no reason to introduce the '__llvm_profile_raw_version' variable into
the module.

5 files changed, 31 insertions, 19 deletions

diff --git a/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp b/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
index fbf9688..ff94fc9 100644
--- a/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
+++ b/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
@@ -405,9 +405,14 @@ static GlobalVariable *createIRLevelProfileFlagVar(Module &M, bool IsCS) {
     ProfileVersion |= VARIANT_MASK_BYTE_COVERAGE;
   if (PGOTemporalInstrumentation)
     ProfileVersion |= VARIANT_MASK_TEMPORAL_PROF;
-  auto IRLevelVersionVariable = new GlobalVariable(
+  assert(!M.global_empty() &&
+         "If a module was instrumented, there must be defined global variables "
+         "at least for the counters.");
+  auto *InsertionPoint = &*M.global_begin();
+  auto *IRLevelVersionVariable = new GlobalVariable(
       M, IntTy64, true, GlobalValue::WeakAnyLinkage,
-      Constant::getIntegerValue(IntTy64, APInt(64, ProfileVersion)), VarName);
+      Constant::getIntegerValue(IntTy64, APInt(64, ProfileVersion)), VarName,
+      InsertionPoint);
   IRLevelVersionVariable->setVisibility(GlobalValue::HiddenVisibility);
   Triple TT(M.getTargetTriple());
   if (TT.supportsCOMDAT()) {
@@ -1829,11 +1834,6 @@ static bool InstrumentAllFunctions(
     Module &M, function_ref<TargetLibraryInfo &(Function &)> LookupTLI,
     function_ref<BranchProbabilityInfo *(Function &)> LookupBPI,
     function_ref<BlockFrequencyInfo *(Function &)> LookupBFI, bool IsCS) {
-  // For the context-sensitve instrumentation, we should have a separated pass
-  // (before LTO/ThinLTO linking) to create these variables.
-  if (!IsCS && !PGOCtxProfLoweringPass::isContextualIRPGOEnabled())
-    createIRLevelProfileFlagVar(M, /*IsCS=*/false);
-
   Triple TT(M.getTargetTriple());
   LLVMContext &Ctx = M.getContext();
   if (!TT.isOSBinFormatELF() && EnableVTableValueProfiling)
@@ -1855,9 +1855,15 @@ static bool InstrumentAllFunctions(
     instrumentOneFunc(F, &M, TLI, BPI, BFI, ComdatMembers, IsCS);
     AnythingInstrumented = true;
   }
+
   if (!AnythingInstrumented)
     return false;
 
+  // For the context-sensitve instrumentation, we should have a separated pass
+  // (before LTO/ThinLTO linking) to create these variables.
+  if (!IsCS && !PGOCtxProfLoweringPass::isContextualIRPGOEnabled())
+    createIRLevelProfileFlagVar(M, /*IsCS=*/false);
+
   return true;
 }
 
diff --git a/llvm/test/Transforms/PGOProfile/declarations_only.ll b/llvm/test/Transforms/PGOProfile/declarations_only.ll
index e7208fc..7a975725 100644
--- a/llvm/test/Transforms/PGOProfile/declarations_only.ll
+++ b/llvm/test/Transforms/PGOProfile/declarations_only.ll
@@ -1,13 +1,8 @@
-; RUN: opt < %s -passes=pgo-instr-gen -S | FileCheck %s --check-prefix=GEN --check-prefix=GEN-COMDAT
+; RUN: opt < %s -passes=pgo-instr-gen -S | FileCheck %s --implicit-check-not='__llvm_profile_raw_version'
 
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
-; GEN-COMDAT: $__llvm_profile_raw_version = comdat any
-; GEN-COMDAT: @__llvm_profile_raw_version = hidden constant i64 {{[0-9]+}}, comdat
-; GEN-NOT: @__profn_test_1 = private constant [6 x i8] c"test_1"
-; GEN-NOT: @__profn_test_2 = private constant [6 x i8] c"test_2"
-
 declare i32 @test_1(i32 %i)
 
 declare i32 @test_2(i32 %i)
diff --git a/llvm/test/Transforms/PGOProfile/global_variables_only.ll b/llvm/test/Transforms/PGOProfile/global_variables_only.ll
index 3bfa29a..46628bf 100644
--- a/llvm/test/Transforms/PGOProfile/global_variables_only.ll
+++ b/llvm/test/Transforms/PGOProfile/global_variables_only.ll
@@ -1,9 +1,6 @@
-; RUN: opt < %s -passes=pgo-instr-gen -S | FileCheck %s --check-prefix=GEN-COMDAT
+; RUN: opt < %s -passes=pgo-instr-gen -S | FileCheck %s --implicit-check-not='__llvm_profile_raw_version'
 
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
-; GEN-COMDAT: $__llvm_profile_raw_version = comdat any
-; GEN-COMDAT: @__llvm_profile_raw_version = hidden constant i64 {{[0-9]+}}, comdat
-
 @var = internal unnamed_addr global [35 x ptr] zeroinitializer, align 16
diff --git a/llvm/test/Transforms/PGOProfile/no_global_variables.ll b/llvm/test/Transforms/PGOProfile/no_global_variables.ll
new file mode 100644
index 0000000..0faa2f3
--- /dev/null
+++ b/llvm/test/Transforms/PGOProfile/no_global_variables.ll
@@ -0,0 +1,15 @@
+; RUN: opt < %s -passes=pgo-instr-gen -S | FileCheck %s --check-prefix=GEN-COMDAT
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+; GEN-COMDAT: $__llvm_profile_raw_version = comdat any
+; GEN-COMDAT: @__llvm_profile_raw_version = hidden constant i64 {{[0-9]+}}, comdat
+
+define i32 @test_1(i32 %i) {
+entry:
+  ret i32 0
+}
+
+define i32 @test_2(i32 %i) {
+entry:
+  ret i32 1
+}
diff --git a/llvm/unittests/Transforms/Instrumentation/PGOInstrumentationTest.cpp b/llvm/unittests/Transforms/Instrumentation/PGOInstrumentationTest.cpp
index cbeaa50..01d17c5 100644
--- a/llvm/unittests/Transforms/Instrumentation/PGOInstrumentationTest.cpp
+++ b/llvm/unittests/Transforms/Instrumentation/PGOInstrumentationTest.cpp
@@ -217,8 +217,7 @@ TEST_P(PGOInstrumentationGenIgnoreTest, NotInstrumented) {
 
   const auto *IRInstrVar =
       M->getNamedGlobal(INSTR_PROF_QUOTE(INSTR_PROF_RAW_VERSION_VAR));
-  EXPECT_THAT(IRInstrVar, NotNull());
-  EXPECT_FALSE(IRInstrVar->isDeclaration());
+  EXPECT_THAT(IRInstrVar, IsNull());
 }
 
 } // end anonymous namespace