[thinlto] Add cold-callsite import heuristic

Summary:
Not tunned up heuristic, but with this small heuristic there is about
+0.10% improvement on SPEC 2006

Reviewers: tejohnson, mehdi_amini, eraman

Subscribers: mehdi_amini, llvm-commits

Differential Revision: https://reviews.llvm.org/D24940

llvm-svn: 282733

llvm/lib/Transforms/IPO/FunctionImport.cpp

@@ -48,10 +48,15 @@ static cl::opt<float>
                       cl::desc("As we import functions, multiply the "
                                "`import-instr-limit` threshold by this factor "
                                "before processing newly imported functions"));
+
 static cl::opt<float> ImportHotMultiplier(
     "import-hot-multiplier", cl::init(3.0), cl::Hidden, cl::value_desc("x"),
-    cl::ZeroOrMore, cl::desc("Multiply the `import-instr-limit` threshold for "
-                             "hot callsites"));
+    cl::desc("Multiply the `import-instr-limit` threshold for hot callsites"));
+
+// FIXME: This multiplier was not really tuned up.
+static cl::opt<float> ImportColdMultiplier(
+    "import-cold-multiplier", cl::init(0), cl::Hidden, cl::value_desc("N"),
+    cl::desc("Multiply the `import-instr-limit` threshold for cold callsites"));
 
 static cl::opt<bool> PrintImports("print-imports", cl::init(false), cl::Hidden,
                                   cl::desc("Print imported functions"));
@@ -285,11 +290,16 @@ static void computeImportForFunction(
       continue;
     }
 
-    // FIXME: Also lower the threshold for cold callsites.
+    auto GetBonusMultiplier = [](CalleeInfo::HotnessType Hotness) -> float {
+      if (Hotness == CalleeInfo::HotnessType::Hot)
+        return ImportHotMultiplier;
+      if (Hotness == CalleeInfo::HotnessType::Cold)
+        return ImportColdMultiplier;
+      return 1.0;
+    };
+
     const auto NewThreshold =
-        Edge.second.Hotness == CalleeInfo::HotnessType::Hot
-            ? Threshold * ImportHotMultiplier
-            : Threshold;
+        Threshold * GetBonusMultiplier(Edge.second.Hotness);
     auto *CalleeSummary = selectCallee(GUID, NewThreshold, Index);
     if (!CalleeSummary) {
       DEBUG(dbgs() << "ignored! No qualifying callee with summary found.\n");

llvm/test/Transforms/FunctionImport/hotness_based_import.ll

@@ -5,12 +5,13 @@
 
 ; Test import with default hot multiplier (3)
 ; RUN: opt -function-import -summary-file %t3.thinlto.bc %t.bc -import-instr-limit=1 --S | FileCheck %s --check-prefix=CHECK --check-prefix=HOT-DEFAULT
-; RUN: opt -function-import -summary-file %t3.thinlto.bc %t.bc -import-instr-limit=1 --S -import-hot-multiplier=3.0 | FileCheck %s --check-prefix=CHECK --check-prefix=HOT-DEFAULT
+; RUN: opt -function-import -summary-file %t3.thinlto.bc %t.bc -import-instr-limit=1 --S -import-hot-multiplier=3.0 -import-cold-multiplier=0.0 | FileCheck %s --check-prefix=CHECK --check-prefix=HOT-DEFAULT
+
 ; HOT-DEFAULT-DAG: define available_externally void @hot1()
 ; HOT-DEFAULT-DAG: define available_externally void @hot2()
-; HOT-DEFAULT-DAG: define available_externally void @cold()
 ; HOT-DEFAULT-DAG: define available_externally void @none1()
 
+; HOT-DEFAULT-NOT: define available_externally void @cold()
 ; HOT-DEFAULT-NOT: define available_externally void @hot3()
 ; HOT-DEFAULT-NOT: define available_externally void @none2()
 ; HOT-DEFAULT-NOT: define available_externally void @none3()
@@ -20,17 +21,26 @@
 ; Test import with hot multiplier 1.0 - treat hot callsites as normal.
 ; RUN: opt -function-import -summary-file %t3.thinlto.bc %t.bc -import-instr-limit=1 -import-hot-multiplier=1.0 --S | FileCheck %s --check-prefix=CHECK --check-prefix=HOT-ONE
 ; HOT-ONE-DAG: define available_externally void @hot1()
-; HOT-ONE-DAG: define available_externally void @cold()
 ; HOT-ONE-DAG: define available_externally void @none1()
+; HOT-ONE-NOT: define available_externally void @cold()
 ; HOT-ONE-NOT: define available_externally void @hot2()
 ; HOT-ONE-NOT: define available_externally void @hot3()
 ; HOT-ONE-NOT: define available_externally void @none2()
 ; HOT-ONE-NOT: define available_externally void @none3()
 ; HOT-ONE-NOT: define available_externally void @cold2()
 
+; RUN: opt -function-import -summary-file %t3.thinlto.bc %t.bc -import-instr-limit=1 -import-hot-multiplier=1.0 -import-cold-multiplier=1.0 --S | FileCheck %s --check-prefix=CHECK --check-prefix=HOT-COLD-ONE
+; HOT-COLD-ONE-DAG: define available_externally void @hot1()
+; HOT-COLD-ONE-DAG: define available_externally void @cold()
+; HOT-COLD-ONE-DAG: define available_externally void @none1()
+; HOT-COLD-ONE-NOT: define available_externally void @hot2()
+; HOT-COLD-ONE-NOT: define available_externally void @hot3()
+; HOT-COLD-ONE-NOT: define available_externally void @none2()
+; HOT-COLD-ONE-NOT: define available_externally void @none3()
+; HOT-COLD-ONE-NOT: define available_externally void @cold2()
 
 ; Test import with hot multiplier 0.0 and high threshold - don't import functions called from hot callsite.
-; RUN: opt -function-import -summary-file %t3.thinlto.bc %t.bc -import-instr-limit=10 -import-hot-multiplier=0.0 --S | FileCheck %s --check-prefix=CHECK --check-prefix=HOT-ZERO
+; RUN: opt -function-import -summary-file %t3.thinlto.bc %t.bc -import-instr-limit=10 -import-hot-multiplier=0.0 -import-cold-multiplier=1.0 --S | FileCheck %s --check-prefix=CHECK --check-prefix=HOT-ZERO
 ; HOT-ZERO-DAG: define available_externally void @cold()
 ; HOT-ZERO-DAG: define available_externally void @none1()
 ; HOT-ZERO-DAG: define available_externally void @none2()