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

[Paul Kirth via Phabricator via llvm-commits]

paulkirth updated this revision to Diff 479473.
paulkirth retitled this revision from "[pgo] Avoid introducing relocations by using private alias" to "Reland "[pgo] Avoid introducing relocations by using private alias""".
paulkirth edited the summary of this revision.
paulkirth added a comment.

Improve test discription and summary


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 +1,40 @@
+; Check that instrprof does not introduce references to discaded sections when
+; using comdats.
+
+; Occasionally, it is possible that the same function can be compiled in
+; different TUs with slightly different linkages, e.g., due to different
+; compiler options. However, if these are comdat functions, a single
+; implementation will be chosen at link time. we want to ensure that the
+; profiling data does not contain a reference to the discarded section.
+
+; 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
+}


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