[PATCH] D137982: [pgo] Avoid introducing relocations by using private alias

[Paul Kirth via Phabricator via llvm-commits]

paulkirth updated this revision to Diff 479469.
paulkirth added a comment.
Herald added a project: Sanitizers.
Herald added a subscriber: Sanitizers.

Add additional test

I'm stil investigating some issues around the references to dropped sections,
but was able to reduce at least one case down to something managable. I've
placed it into the runtime tests, since it requires a linker to detect.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D137982/new/

https://reviews.llvm.org/D137982

Files:
  compiler-rt/test/profile/instrprof-discarded-comdat.ll
  llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
  llvm/test/Transforms/PGOProfile/prof_avoid_relocs.ll


Index: llvm/test/Transforms/PGOProfile/prof_avoid_relocs.ll
===================================================================
--- /dev/null
+++ 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
+}
+
Index: llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
===================================================================
--- llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
+++ llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
@@ -1014,9 +1014,17 @@
   };
   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)
Index: compiler-rt/test/profile/instrprof-discarded-comdat.ll
===================================================================
--- /dev/null
+++ compiler-rt/test/profile/instrprof-discarded-comdat.ll
@@ -0,0 +1,34 @@
+; Check that instrprof does not introduce references that can be discarded
+; when using comdats
+
+; RUN: split-file %s %t
+
+; RUN: opt %t/a1.ll -disable-preinline -passes="pgo-instr-gen,instrprof" -S | llc --filetype=obj -o %t/a1.o
+; RUN: opt %t/a2.ll -passes="pgo-instr-gen,instrprof" -S | llc --filetype=obj -o %t/a2.o
+
+; RUN: %clang -fPIC -shared -o %t/liba.so %t/a1.o %t/a2.o 2>&1 | FileCheck %s
+
+; Ensure that we don't get an error when linking
+; CHECK-NOT: relocation refers to a discarded section: .text._ZN1CIiE1fEi
+
+;--- a1.ll
+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"
+$_ZN1CIiE1fEi = comdat any
+
+define weak void @_ZN1CIiE1fEi(ptr %this, i32 %x) comdat {
+entry:
+  ret void
+}
+
+
+
+;--- a2.ll
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+$_ZN1CIiE1fEi = comdat any
+
+define linkonce_odr void @_ZN1CIiE1fEi(ptr %this, i32 %x) comdat {
+entry:
+  ret void
+}


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D137982.479469.patch
Type: text/x-patch
Size: 3470 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20221202/ca060ad5/attachment.bin>