Runtime flag to control branch funnel threshold

[vitalybuka]

ping

[pcc]

LGTM

llvm/trunk/lib/Transforms/IPO/WholeProgramDevirt.cpp

static cl::opt<std::string> ClReadSummary(
     cl::desc("Read summary from given YAML file before running pass"),
     cl::Hidden);
 
 static cl::opt<std::string> ClWriteSummary(
     "wholeprogramdevirt-write-summary",
     cl::desc("Write summary to given YAML file after running pass"),
     cl::Hidden);
 
+static cl::opt<int> ClThreshold("wholeprogramdevirt-branch-funnel-threshold",
+                                cl::Hidden, cl::init(10), cl::ZeroOrMore,
+                                cl::desc("Maximum number of call targets per "
+                                         "call site to enable branch funnels"));
+
 // Find the minimum offset that we may store a value of size Size bits at. If
 // IsAfter is set, look for an offset before the object, otherwise look for an
 // offset after the object.
 uint64_t
 wholeprogramdevirt::findLowestOffset(ArrayRef<VirtualCallTarget> Targets,
                                      bool IsAfter, uint64_t Size) {
   // Find a minimum offset taking into account only vtable sizes.
   uint64_t MinByte = 0;

 
 void DevirtModule::tryICallBranchFunnel(
     MutableArrayRef<VirtualCallTarget> TargetsForSlot, VTableSlotInfo &SlotInfo,
     WholeProgramDevirtResolution *Res, VTableSlot Slot) {
   Triple T(M.getTargetTriple());
   if (T.getArch() != Triple::x86_64)
     return;
 
-  const unsigned kBranchFunnelThreshold = 10;
-  if (TargetsForSlot.size() > kBranchFunnelThreshold)
+  if (TargetsForSlot.size() > ClThreshold)
     return;
 
   bool HasNonDevirt = !SlotInfo.CSInfo.AllCallSitesDevirted;
   if (!HasNonDevirt)
     for (auto &P : SlotInfo.ConstCSInfo)
       if (!P.second.AllCallSitesDevirted) {
         HasNonDevirt = true;
         break;

llvm/trunk/test/Transforms/WholeProgramDevirt/branch-funnel-threshold.ll

+; RUN: opt -wholeprogramdevirt -wholeprogramdevirt-summary-action=export -wholeprogramdevirt-read-summary=%S/Inputs/export.yaml -wholeprogramdevirt-write-summary=%t -wholeprogramdevirt-branch-funnel-threshold=1 -S -o - %s | not grep @llvm.icall.branch.funnel | count 0
+
+; RUN: opt -wholeprogramdevirt -wholeprogramdevirt-summary-action=export -wholeprogramdevirt-read-summary=%S/Inputs/export.yaml -wholeprogramdevirt-write-summary=%t -wholeprogramdevirt-branch-funnel-threshold=10 -S -o - %s | grep @llvm.icall.branch.funnel | count 4
+
+; RUN: opt -wholeprogramdevirt -wholeprogramdevirt-summary-action=export -wholeprogramdevirt-read-summary=%S/Inputs/export.yaml -wholeprogramdevirt-write-summary=%t -wholeprogramdevirt-branch-funnel-threshold=100 -S -o - %s | grep @llvm.icall.branch.funnel | count 5
+
+target datalayout = "e-p:64:64"
+target triple = "x86_64-unknown-linux-gnu"
+
+@vt1_1 = constant [1 x i8*] [i8* bitcast (i32 (i8*, i32)* @vf1_1 to i8*)], !type !0
+@vt1_2 = constant [1 x i8*] [i8* bitcast (i32 (i8*, i32)* @vf1_2 to i8*)], !type !0
+
+declare i32 @vf1_1(i8* %this, i32 %arg)
+declare i32 @vf1_2(i8* %this, i32 %arg)
+
+@vt2_1 = constant [1 x i8*] [i8* bitcast (i32 (i8*, i32)* @vf2_1 to i8*)], !type !1
+@vt2_2 = constant [1 x i8*] [i8* bitcast (i32 (i8*, i32)* @vf2_2 to i8*)], !type !1
+@vt2_3 = constant [1 x i8*] [i8* bitcast (i32 (i8*, i32)* @vf2_3 to i8*)], !type !1
+@vt2_4 = constant [1 x i8*] [i8* bitcast (i32 (i8*, i32)* @vf2_4 to i8*)], !type !1
+@vt2_5 = constant [1 x i8*] [i8* bitcast (i32 (i8*, i32)* @vf2_5 to i8*)], !type !1
+@vt2_6 = constant [1 x i8*] [i8* bitcast (i32 (i8*, i32)* @vf2_6 to i8*)], !type !1
+@vt2_7 = constant [1 x i8*] [i8* bitcast (i32 (i8*, i32)* @vf2_7 to i8*)], !type !1
+@vt2_8 = constant [1 x i8*] [i8* bitcast (i32 (i8*, i32)* @vf2_8 to i8*)], !type !1
+@vt2_9 = constant [1 x i8*] [i8* bitcast (i32 (i8*, i32)* @vf2_9 to i8*)], !type !1
+@vt2_10 = constant [1 x i8*] [i8* bitcast (i32 (i8*, i32)* @vf2_10 to i8*)], !type !1
+@vt2_11 = constant [1 x i8*] [i8* bitcast (i32 (i8*, i32)* @vf2_11 to i8*)], !type !1
+
+declare i32 @vf2_1(i8* %this, i32 %arg)
+declare i32 @vf2_2(i8* %this, i32 %arg)
+declare i32 @vf2_3(i8* %this, i32 %arg)
+declare i32 @vf2_4(i8* %this, i32 %arg)
+declare i32 @vf2_5(i8* %this, i32 %arg)
+declare i32 @vf2_6(i8* %this, i32 %arg)
+declare i32 @vf2_7(i8* %this, i32 %arg)
+declare i32 @vf2_8(i8* %this, i32 %arg)
+declare i32 @vf2_9(i8* %this, i32 %arg)
+declare i32 @vf2_10(i8* %this, i32 %arg)
+declare i32 @vf2_11(i8* %this, i32 %arg)
+
+@vt3_1 = constant [1 x i8*] [i8* bitcast (i32 (i8*, i32)* @vf3_1 to i8*)], !type !2
+@vt3_2 = constant [1 x i8*] [i8* bitcast (i32 (i8*, i32)* @vf3_2 to i8*)], !type !2
+
+declare i32 @vf3_1(i8* %this, i32 %arg)
+declare i32 @vf3_2(i8* %this, i32 %arg)
+
+@vt4_1 = constant [1 x i8*] [i8* bitcast (i32 (i8*, i32)* @vf4_1 to i8*)], !type !3
+@vt4_2 = constant [1 x i8*] [i8* bitcast (i32 (i8*, i32)* @vf4_2 to i8*)], !type !3
+
+declare i32 @vf4_1(i8* %this, i32 %arg)
+declare i32 @vf4_2(i8* %this, i32 %arg)
+
+define i32 @fn1(i8* %obj) #0 {
+  %vtableptr = bitcast i8* %obj to [1 x i8*]**
+  %vtable = load [1 x i8*]*, [1 x i8*]** %vtableptr
+  %vtablei8 = bitcast [1 x i8*]* %vtable to i8*
+  %p = call i1 @llvm.type.test(i8* %vtablei8, metadata !"typeid1")
+  call void @llvm.assume(i1 %p)
+  %fptrptr = getelementptr [1 x i8*], [1 x i8*]* %vtable, i32 0, i32 0
+  %fptr = load i8*, i8** %fptrptr
+  %fptr_casted = bitcast i8* %fptr to i32 (i8*, i32)*
+  %result = call i32 %fptr_casted(i8* %obj, i32 1)
+  ret i32 %result
+}
+
+define i32 @fn2(i8* %obj) #0 {
+  %vtableptr = bitcast i8* %obj to [1 x i8*]**
+  %vtable = load [1 x i8*]*, [1 x i8*]** %vtableptr
+  %vtablei8 = bitcast [1 x i8*]* %vtable to i8*
+  %p = call i1 @llvm.type.test(i8* %vtablei8, metadata !"typeid2")
+  call void @llvm.assume(i1 %p)
+  %fptrptr = getelementptr [1 x i8*], [1 x i8*]* %vtable, i32 0, i32 0
+  %fptr = load i8*, i8** %fptrptr
+  %fptr_casted = bitcast i8* %fptr to i32 (i8*, i32)*
+  %result = call i32 %fptr_casted(i8* %obj, i32 1)
+  ret i32 %result
+}
+
+define i32 @fn3(i8* %obj) #0 {
+  %vtableptr = bitcast i8* %obj to [1 x i8*]**
+  %vtable = load [1 x i8*]*, [1 x i8*]** %vtableptr
+  %vtablei8 = bitcast [1 x i8*]* %vtable to i8*
+  %p = call i1 @llvm.type.test(i8* %vtablei8, metadata !4)
+  call void @llvm.assume(i1 %p)
+  %fptrptr = getelementptr [1 x i8*], [1 x i8*]* %vtable, i32 0, i32 0
+  %fptr = load i8*, i8** %fptrptr
+  %fptr_casted = bitcast i8* %fptr to i32 (i8*, i32)*
+  %result = call i32 %fptr_casted(i8* %obj, i32 1)
+  ret i32 %result
+}
+
+declare i1 @llvm.type.test(i8*, metadata)
+declare void @llvm.assume(i1)
+
+!0 = !{i32 0, !"typeid1"}
+!1 = !{i32 0, !"typeid2"}
+!2 = !{i32 0, !"typeid3"}
+!3 = !{i32 0, !4}
+!4 = distinct !{}
+
+attributes #0 = { "target-features"="+retpoline" }