[llvm] 2b8917f - [pgo] Avoid introducing relocations by using private alias

[Paul Kirth via llvm-commits]

Author: Paul Kirth
Date: 2022-11-15T16:05:24Z
New Revision: 2b8917f8ad792c4c484975b82039bbdebe556881

URL: https://github.com/llvm/llvm-project/commit/2b8917f8ad792c4c484975b82039bbdebe556881
DIFF: https://github.com/llvm/llvm-project/commit/2b8917f8ad792c4c484975b82039bbdebe556881.diff

LOG: [pgo] Avoid introducing relocations by using private alias

Instead of using the public, interposable symbol, we can use a private
alias and avoid relocations and addends.

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D137982

Added: 
    llvm/test/Transforms/PGOProfile/prof_avoid_relocs.ll

Modified: 
    llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp b/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
index 3af3f908ea5b2..569156dd3e239 100644
--- a/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
+++ b/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
@@ -1014,9 +1014,17 @@ InstrProfiling::getOrCreateRegionCounters(InstrProfInstBase *Inc) {
   };
   auto *DataTy = StructType::get(Ctx, makeArrayRef(DataTypes));
 
-  Constant *FunctionAddr = shouldRecordFunctionAddr(Fn)
-                               ? ConstantExpr::getBitCast(Fn, Int8PtrTy)
-                               : ConstantPointerNull::get(Int8PtrTy);
+  Constant *FunctionAddr;
+  if (shouldRecordFunctionAddr(Fn)) {
+    // When possible use a private alias to avoid relocations
+    Constant *Addr = !Fn->isDeclarationForLinker()
+                         ? static_cast<Constant *>(GlobalAlias::create(
+                               GlobalValue::PrivateLinkage, Fn->getName(), Fn))
+                         : Fn;
+    FunctionAddr = ConstantExpr::getBitCast(Addr, Int8PtrTy);
+  } else {
+    FunctionAddr = ConstantPointerNull::get(Int8PtrTy);
+  }
 
   Constant *Int16ArrayVals[IPVK_Last + 1];
   for (uint32_t Kind = IPVK_First; Kind <= IPVK_Last; ++Kind)

diff  --git a/llvm/test/Transforms/PGOProfile/prof_avoid_relocs.ll b/llvm/test/Transforms/PGOProfile/prof_avoid_relocs.ll
new file mode 100644
index 0000000000000..c77dd21679631
--- /dev/null
+++ b/llvm/test/Transforms/PGOProfile/prof_avoid_relocs.ll
@@ -0,0 +1,23 @@
+; RUN: opt -S -passes=pgo-instr-gen,instrprof < %s | FileCheck %s
+
+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"
+
+; Test that we use private aliases to reference function addresses inside profile data
+
+; CHECK: @__profd_foo = private global {{.*}}, ptr @foo.1,
+; CHECK-NOT: @__profd_foo = private global {{.*}}, ptr @foo,
+; CHECK: @foo.1 = private alias i32 (i32), ptr @foo
+
+define i32 @foo(i32 %0) {
+; CHECK-LABEL: @foo(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[PGOCOUNT:%.*]] = load i64, ptr @__profc_foo, align 8
+; CHECK-NEXT:    [[TMP1:%.*]] = add i64 [[PGOCOUNT]], 1
+; CHECK-NEXT:    store i64 [[TMP1]], ptr @__profc_foo, align 8
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  ret i32 0
+}
+