[clang] 25c3032 - [AIX] Change the linkage of profiling counter/data to be private

[Jinsong Ji via cfe-commits]

Author: Jinsong Ji
Date: 2021-09-29T00:47:25Z
New Revision: 25c30324e953c1c0011d1ab7529991db5c6ba741

URL: https://github.com/llvm/llvm-project/commit/25c30324e953c1c0011d1ab7529991db5c6ba741
DIFF: https://github.com/llvm/llvm-project/commit/25c30324e953c1c0011d1ab7529991db5c6ba741.diff

LOG: [AIX] Change the linkage of profiling counter/data to be private

We generate symbols like `profc`/`profd` for each function, and put them into csects.
When there are weak functions,  we generate weak symbols for the functions as well,
with ELF (and some others),  linker (binder) will discard and only keep one copy of the weak symbols.

However, on AIX, the current binder can NOT discard the weak symbols if we put all of them into the same csect,
as binder can NOT discard a subset of a csect.

This creates a unique challenge for using those symbols to calculate some relative offsets.

This patch changed the linkage of `profc`/`profd` symbols to be private, so that all the profc/profd for each weak symbol will be *local* to objects, and all kept in the csect, so we won't have problem. Although only one of the counters will be used, all the pointer in the profd is correct.

The downside is that we won't be able to discard the duplicated counters and profile data,
but those can not be discarded even if we keep the weak linkage,
due to the binder limitation of not discarding a subsect of the csect either .

Reviewed By: Whitney, MaskRay

Differential Revision: https://reviews.llvm.org/D110422

Added: 
    

Modified: 
    clang/test/Profile/cxx-templates.cpp
    llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
    llvm/test/Instrumentation/InstrProfiling/profiling.ll

Removed: 
    


################################################################################
diff  --git a/clang/test/Profile/cxx-templates.cpp b/clang/test/Profile/cxx-templates.cpp
index 7af6660f521db..9f8c5a0bcf593 100644
--- a/clang/test/Profile/cxx-templates.cpp
+++ b/clang/test/Profile/cxx-templates.cpp
@@ -10,8 +10,10 @@
 // RUN: FileCheck --input-file=%tuse -check-prefix=T0USE -check-prefix=ALL %s
 // RUN: FileCheck --input-file=%tuse -check-prefix=T100USE -check-prefix=ALL %s
 
-// T0GEN: @[[T0C:__profc__Z4loopILj0EEvv]] = linkonce_odr {{(hidden|dso_local)}} global [2 x i64] zeroinitializer
-// T100GEN: @[[T100C:__profc__Z4loopILj100EEvv]] = linkonce_odr {{(hidden|dso_local)}} global [2 x i64] zeroinitializer
+// The linkage can be target dependent, so accept all linkage here,
+// the linkage tests for 
diff erent target are in llvm/test/Instrumentation/InstrProfiling/profiling.ll
+// T0GEN: @[[T0C:__profc__Z4loopILj0EEvv]] = {{.*}} global [2 x i64] zeroinitializer
+// T100GEN: @[[T100C:__profc__Z4loopILj100EEvv]] = {{.*}} global [2 x i64] zeroinitializer
 
 // T0GEN-LABEL: define linkonce_odr {{.*}}void @_Z4loopILj0EEvv()
 // T0USE-LABEL: define linkonce_odr {{.*}}void @_Z4loopILj0EEvv()

diff  --git a/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp b/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
index bdeb7c8cbbb15..fe93e27075044 100644
--- a/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
+++ b/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
@@ -862,6 +862,15 @@ InstrProfiling::getOrCreateRegionCounters(InstrProfIncrementInst *Inc) {
   GlobalValue::LinkageTypes Linkage = NamePtr->getLinkage();
   GlobalValue::VisibilityTypes Visibility = NamePtr->getVisibility();
 
+  // Due to the limitation of binder as of 2021/09/28, the duplicate weak
+  // symbols in the same csect won't be discarded. When there are duplicate weak
+  // symbols, we can NOT guarantee that the relocations get resolved to the
+  // intended weak symbol, so we can not ensure the correctness of the relative
+  // CounterPtr, so we have to use private linkage for counter and data symbols.
+  if (TT.isOSBinFormatXCOFF()) {
+    Linkage = GlobalValue::PrivateLinkage;
+    Visibility = GlobalValue::DefaultVisibility;
+  }
   // Move the name variable to the right section. Place them in a COMDAT group
   // if the associated function is a COMDAT. This will make sure that only one
   // copy of counters of the COMDAT function will be emitted after linking. Keep

diff  --git a/llvm/test/Instrumentation/InstrProfiling/profiling.ll b/llvm/test/Instrumentation/InstrProfiling/profiling.ll
index e4bc8387ef294..8138552b42d59 100644
--- a/llvm/test/Instrumentation/InstrProfiling/profiling.ll
+++ b/llvm/test/Instrumentation/InstrProfiling/profiling.ll
@@ -45,8 +45,8 @@ define void @foo() {
 ; MACHO: @__profd_foo_weak = weak hidden global
 ; COFF: @__profc_foo_weak = weak hidden global
 ; COFF: @__profd_foo_weak = private global
-; XCOFF: @__profc_foo_weak = weak hidden global
-; XCOFF: @__profd_foo_weak = weak hidden global
+; XCOFF: @__profc_foo_weak = private global
+; XCOFF: @__profd_foo_weak = private global
 define weak void @foo_weak() {
   call void @llvm.instrprof.increment(i8* getelementptr inbounds ([8 x i8], [8 x i8]* @__profn_foo_weak, i32 0, i32 0), i64 0, i32 1, i32 0)
   ret void
@@ -71,8 +71,8 @@ define internal void @foo_internal() {
 ; MACHO: @__profd_foo_inline = linkonce_odr hidden global
 ; COFF: @__profc_foo_inline = linkonce_odr hidden global{{.*}} section ".lprfc$M", align 8
 ; COFF: @__profd_foo_inline = private global{{.*}} section ".lprfd$M", align 8
-; XCOFF: @__profc_foo_inline = linkonce_odr hidden global
-; XCOFF: @__profd_foo_inline = linkonce_odr hidden global
+; XCOFF: @__profc_foo_inline = private global
+; XCOFF: @__profd_foo_inline = private global
 define linkonce_odr void @foo_inline() {
   call void @llvm.instrprof.increment(i8* getelementptr inbounds ([10 x i8], [10 x i8]* @__profn_foo_inline, i32 0, i32 0), i64 0, i32 1, i32 0)
   ret void
@@ -84,8 +84,8 @@ define linkonce_odr void @foo_inline() {
 ; MACHO: @__profd_foo_extern = linkonce_odr hidden global
 ; COFF: @__profc_foo_extern = linkonce_odr hidden global {{.*}}section ".lprfc$M", comdat, align 8
 ; COFF: @__profd_foo_extern = private global {{.*}}section ".lprfd$M", comdat($__profc_foo_extern), align 8
-; XCOFF: @__profc_foo_extern = linkonce_odr hidden global
-; XCOFF: @__profd_foo_extern = linkonce_odr hidden global
+; XCOFF: @__profc_foo_extern = private global
+; XCOFF: @__profd_foo_extern = private global
 define available_externally void @foo_extern() {
   call void @llvm.instrprof.increment(i8* getelementptr inbounds ([10 x i8], [10 x i8]* @__profn_foo_extern, i32 0, i32 0), i64 0, i32 1, i32 0)
   ret void