From: Teresa Johnson <tejohnson@google.com>
Date: Tue, 24 Nov 2015 22:55:46 +0000 (+0000)
Subject: [ThinLTO] Add option to limit importing based on instruction count
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=f65b5feba490438fca8b365dc84cee69f7d97ec7;p=oota-llvm.git

[ThinLTO] Add option to limit importing based on instruction count

Add a simple initial heuristic to control importing based on the number
of instructions recorded in the function's summary. Add option to
control the limit, and test using option.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@254036 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/IPO/FunctionImport.cpp b/lib/Transforms/IPO/FunctionImport.cpp
index 1f88da5e12a..ab0f7114957 100644
--- a/lib/Transforms/IPO/FunctionImport.cpp
+++ b/lib/Transforms/IPO/FunctionImport.cpp
@@ -28,6 +28,11 @@ using namespace llvm;
 
 #define DEBUG_TYPE "function-import"
 
+/// Limit on instruction count of imported functions.
+static cl::opt<unsigned> ImportInstrLimit(
+    "import-instr-limit", cl::init(100), cl::Hidden, cl::value_desc("N"),
+    cl::desc("Only import functions with less than N instructions"));
+
 // Load lazily a module from \p FileName in \p Context.
 static std::unique_ptr<Module> loadFile(const std::string &FileName,
                                         LLVMContext &Context) {
@@ -124,6 +129,13 @@ bool FunctionImporter::importFunctions(Module &M) {
       llvm_unreachable("Missing summary");
     }
 
+    if (Summary->instCount() > ImportInstrLimit) {
+      dbgs() << "Skip import of " << CalledFunctionName << " with "
+             << Summary->instCount() << " instructions (limit "
+             << ImportInstrLimit << ")\n";
+      continue;
+    }
+
     //
     // No profitability notion right now, just import all the time...
     //
diff --git a/test/Transforms/FunctionImport/funcimport.ll b/test/Transforms/FunctionImport/funcimport.ll
index 553d05bfcf3..57452b1ec53 100644
--- a/test/Transforms/FunctionImport/funcimport.ll
+++ b/test/Transforms/FunctionImport/funcimport.ll
@@ -4,7 +4,11 @@
 ; RUN: llvm-lto -thinlto -o %t3 %t.bc %t2.bc
 
 ; Do the import now
-; RUN: opt -function-import -summary-file %t3.thinlto.bc %s -S | FileCheck %s
+; RUN: opt -function-import -summary-file %t3.thinlto.bc %s -S | FileCheck %s --check-prefix=CHECK --check-prefix=INSTLIMDEF
+
+; Test import with smaller instruction limit
+; RUN: opt -function-import -summary-file %t3.thinlto.bc %s -import-instr-limit=5 -S | FileCheck %s --check-prefix=CHECK --check-prefix=INSTLIM5
+; INSTLIM5-NOT: @staticfunc.llvm.2
 
 define i32 @main() #0 {
 entry:
@@ -28,14 +32,15 @@ declare void @weakalias(...) #1
 ; CHECK-DAG: define available_externally void @globalfunc2()
 declare void @analias(...) #1
 
-; CHECK-DAG: define available_externally i32 @referencestatics(i32 %i)
+; INSTLIMDEF-DAG: define available_externally i32 @referencestatics(i32 %i)
+; INSTLIM5-DAG: declare i32 @referencestatics(...)
 declare i32 @referencestatics(...) #1
 
 ; The import of referencestatics will expose call to staticfunc that
 ; should in turn be imported as a promoted/renamed and hidden function.
 ; Ensure that the call is to the properly-renamed function.
-; CHECK-DAG: %call = call i32 @staticfunc.llvm.2()
-; CHECK-DAG: define available_externally hidden i32 @staticfunc.llvm.2()
+; INSTLIMDEF-DAG: %call = call i32 @staticfunc.llvm.2()
+; INSTLIMDEF-DAG: define available_externally hidden i32 @staticfunc.llvm.2()
 
 ; CHECK-DAG: define available_externally i32 @referenceglobals(i32 %i)
 declare i32 @referenceglobals(...) #1