llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-pgo
@llvm/pr-subscribers-lto
Author: Mingming Liu (minglotus-6)
<details>
<summary>Changes</summary>
Given a ref chain `mod1:func_foo -> mod2:func_bar -> mod2:local-var`, when `func_bar` gets imported into `mod1`, `local-var` doesn't get imported by default. Compiler checks / requires the module of 'local-var' is the same as the function that starts the import (`mod1:func_foo`). This is to prevent mis-compilation when both `mod1` and `mod2` has `local-var` of the same name, and cpp files are compiled without full path (`//path//to/file.cpp`).
This patch introduces an option for compiler user. If compiler user can guarantee that all files are compiled with full paths, they can set this option on to get `mod2:local-var` imported into `mod1` for the case above.
Test:
* A/B testing this option alone gives -0.16% statistically consistent cpu cycle reduction on one search workload (no throughput increase)
* Testing it together with existing more-efficient ICP bumps the throughput increase by a margin (0.05%~0.1%)
---
Full diff: https://github.com/llvm/llvm-project/pull/100448.diff
2 Files Affected:
- (modified) compiler-rt/test/profile/Linux/instrprof-vtable-value-prof.cpp (+22-8)
- (modified) llvm/lib/Transforms/IPO/FunctionImport.cpp (+14)
``````````diff
diff --git a/compiler-rt/test/profile/Linux/instrprof-vtable-value-prof.cpp b/compiler-rt/test/profile/Linux/instrprof-vtable-value-prof.cpp
index 411640fc5176d..4ef7b2da2f572 100644
--- a/compiler-rt/test/profile/Linux/instrprof-vtable-value-prof.cpp
+++ b/compiler-rt/test/profile/Linux/instrprof-vtable-value-prof.cpp
@@ -1,3 +1,4 @@
+
// REQUIRES: lld, lld-available
// Building the instrumented binary will fail because lld doesn't support
@@ -5,7 +6,7 @@
// ld.lld: error: /lib/../lib64/Scrt1.o: ABI version 1 is not supported
// UNSUPPORTED: ppc && host-byteorder-big-endian
-// RUN: rm -rf %t && mkdir %t && cd %t
+// RUN: rm -rf %t && split-file %s %t && cd %t
// RUN: %clangxx_pgogen -fuse-ld=lld -O2 -fprofile-generate=. -mllvm -enable-vtable-value-profiling %s -o test
// RUN: env LLVM_PROFILE_FILE=test.profraw ./test
@@ -141,18 +142,19 @@
// RUN: -g -flto=thin -fwhole-program-vtables -fno-split-lto-unit -O2 \
// RUN: -mllvm -enable-vtable-value-profiling -Wl,-mllvm,-enable-vtable-value-profiling \
// RUN: -mllvm -enable-vtable-profile-use \
+// RUN: -Wl,-plugin-opt,-import-assume-unique-local \
// RUN: -Wl,-mllvm,-enable-vtable-profile-use -Rpass=pgo-icall-prom \
// RUN: -Wl,-mllvm,-print-after=pgo-icall-prom \
// RUN: -Wl,-mllvm,-filter-print-funcs=main %s 2>&1 \
// RUN: | FileCheck %s --check-prefixes=REMARK,IR --implicit-check-not="!VP"
// For the indirect call site `ptr->func`
-// REMARK: instrprof-vtable-value-prof.cpp:226:19: Promote indirect call to _ZN12_GLOBAL__N_18Derived24funcEii with count 150 out of 200, sink 1 instruction(s) and compare 1 vtable(s): {_ZTVN12_GLOBAL__N_18Derived2E}
-// REMARK: instrprof-vtable-value-prof.cpp:226:19: Promote indirect call to _ZN8Derived14funcEii with count 50 out of 50, sink 1 instruction(s) and compare 1 vtable(s): {_ZTV8Derived1}
+// REMARK: instrprof-vtable-value-prof.cpp:240:19: Promote indirect call to _ZN12_GLOBAL__N_18Derived24funcEii with count 150 out of 200, sink 1 instruction(s) and compare 1 vtable(s): {_ZTVN12_GLOBAL__N_18Derived2E}
+// REMARK: instrprof-vtable-value-prof.cpp:240:19: Promote indirect call to _ZN8Derived14funcEii with count 50 out of 50, sink 1 instruction(s) and compare 1 vtable(s): {_ZTV8Derived1}
//
// For the indirect call site `delete ptr`
-// REMARK: instrprof-vtable-value-prof.cpp:228:5: Promote indirect call to _ZN12_GLOBAL__N_18Derived2D0Ev with count 750 out of 1000, sink 2 instruction(s) and compare 1 vtable(s): {_ZTVN12_GLOBAL__N_18Derived2E}
-// REMARK: instrprof-vtable-value-prof.cpp:228:5: Promote indirect call to _ZN8Derived1D0Ev with count 250 out of 250, sink 2 instruction(s) and compare 1 vtable(s): {_ZTV8Derived1}
+// REMARK: instrprof-vtable-value-prof.cpp:242:5: Promote indirect call to _ZN12_GLOBAL__N_18Derived2D0Ev with count 750 out of 1000, sink 2 instruction(s) and compare 1 vtable(s): {_ZTVN12_GLOBAL__N_18Derived2E}
+// REMARK: instrprof-vtable-value-prof.cpp:242:5: Promote indirect call to _ZN8Derived1D0Ev with count 250 out of 250, sink 2 instruction(s) and compare 1 vtable(s): {_ZTV8Derived1}
// The IR matchers for indirect callsite `ptr->func`.
// IR-LABEL: @main
@@ -185,6 +187,7 @@
// IR: [[MERGE0]]:
// IR: [[RES2:%.*]] = phi i32 [ [[RES1]], %[[MERGE1]] ], [ [[RESBB1]], %[[BB1]] ]
+//--- lib.h
#include <stdio.h>
#include <stdlib.h>
class Base {
@@ -193,21 +196,31 @@ class Base {
virtual ~Base() {};
};
+
class Derived1 : public Base {
public:
- int func(int a, int b) override { return a * b; }
+ int func(int a, int b) override;
~Derived1() {}
};
namespace {
class Derived2 : public Base {
public:
- int func(int a, int b) override { return a * (a - b); }
+ int func(int a, int b) override;
~Derived2() {}
};
} // namespace
-__attribute__((noinline)) Base *createType(int a) {
+
+__attribute__((noinline)) Base *createType(int a);
+
+//-- lib.cpp
+
+int Derived1::func(int a, int b) { return a * b; }
+
+int Derived2::func(int a, int b) { return a * (a - b); }
+
+Base *createType(int a) {
Base *base = nullptr;
if (a % 4 == 0)
base = new Derived1();
@@ -216,6 +229,7 @@ __attribute__((noinline)) Base *createType(int a) {
return base;
}
+//--- main.cpp
int main(int argc, char **argv) {
int sum = 0;
for (int i = 0; i < 1000; i++) {
diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index 038785114a0cf..839c09fa9d586 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -174,6 +174,18 @@ static cl::opt<std::string> WorkloadDefinitions(
"}"),
cl::Hidden);
+static cl::opt<bool> ImportAssumeUniqueLocal(
+ "import-assume-unique-local", cl::init(false),
+ cl::desc(
+ "By default, a local-linkage global variable won't be imported in the "
+ "edge mod1:func -> mod2:func_bar -> mod2:local-var since compiler "
+ "cannot assume mod2 is compiled with full path or local-var has a "
+ "unique GUID. "
+ "Set this option to true will help cross-module import of such "
+ "variables. But it is only safe if the compiler user specify the full "
+ "module path."),
+ cl::Hidden);
+
namespace llvm {
extern cl::opt<bool> EnableMemProfContextDisambiguation;
}
@@ -367,6 +379,8 @@ class GlobalsImporter final {
// was not distinguishing path.
auto LocalNotInModule =
[&](const GlobalValueSummary *RefSummary) -> bool {
+ if (ImportAssumeUniqueLocal)
+ return false;
return GlobalValue::isLocalLinkage(RefSummary->linkage()) &&
RefSummary->modulePath() != Summary.modulePath();
};
``````````
</details>
https://github.com/llvm/llvm-project/pull/100448