[compiler-rt] [llvm] [CallPromotionUtils]Implement conditional indirect call promotion with vtable-based comparison (PR #81378)

[David Li via llvm-commits]

================
@@ -368,3 +371,115 @@ declare %struct2 @_ZN4Impl3RunEv(%class.Impl* %this)
   bool IsPromoted = tryPromoteCall(*CI);
   EXPECT_FALSE(IsPromoted);
 }
+
+TEST(CallPromotionUtilsTest, getVTableAddressPointOffset) {
+  LLVMContext C;
+  std::unique_ptr<Module> M = parseIR(C,
+                                      R"IR(
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+ at _ZTV8Derived2 = constant { [3 x ptr], [3 x ptr], [4 x ptr] } { [3 x ptr] [ptr null, ptr null, ptr @_ZN5Base35func3Ev], [3 x ptr] [ptr inttoptr (i64 -8 to ptr), ptr null, ptr @_ZN5Base25func2Ev], [4 x ptr] [ptr inttoptr (i64 -16 to ptr), ptr null, ptr @_ZN5Base15func0Ev, ptr @_ZN5Base15func1Ev] }
+
+declare i32 @_ZN5Base15func1Ev(ptr)
+declare i32 @_ZN5Base25func2Ev(ptr)
+declare i32 @_ZN5Base15func0Ev(ptr)
+declare void @_ZN5Base35func3Ev(ptr)
+)IR");
+  GlobalVariable *GV = M->getGlobalVariable("_ZTV8Derived2");
+
+  for (auto [AddressPointOffset, Index] :
+       {std::pair{16, 0}, {40, 1}, {64, 2}}) {
+    Constant *AddressPoint =
+        getVTableAddressPointOffset(GV, AddressPointOffset);
+
+    SmallVector<Constant *> Indices = {
+        llvm::ConstantInt::get(Type::getInt32Ty(C), 0U),
+        llvm::ConstantInt::get(Type::getInt32Ty(C), Index),
+        llvm::ConstantInt::get(Type::getInt32Ty(C), 2U)};
+    EXPECT_EQ(dyn_cast<ConstantExpr>(AddressPoint),
+              ConstantExpr::getInBoundsGetElementPtr(GV->getValueType(), GV,
+                                                     Indices));
+  }
+}
+
+TEST(CallPromotionUtilsTest, promoteCallWithVTableCmp) {
+  LLVMContext C;
+  std::unique_ptr<Module> M = parseIR(C,
+                                      R"IR(
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+ at _ZTV5Base1 = constant { [4 x ptr] } { [4 x ptr] [ptr null, ptr null, ptr @_ZN5Base15func0Ev, ptr @_ZN5Base15func1Ev] }, !type !0
+ at _ZTV8Derived1 = constant { [4 x ptr], [3 x ptr] } { [4 x ptr] [ptr inttoptr (i64 -8 to ptr), ptr null, ptr @_ZN5Base15func0Ev, ptr @_ZN5Base15func1Ev], [3 x ptr] [ptr null, ptr null, ptr @_ZN5Base25func2Ev] }, !type !0, !type !1, !type !2
+ at _ZTV8Derived2 = constant { [3 x ptr], [3 x ptr], [4 x ptr] } { [3 x ptr] [ptr null, ptr null, ptr @_ZN5Base35func3Ev], [3 x ptr] [ptr inttoptr (i64 -8 to ptr), ptr null, ptr @_ZN5Base25func2Ev], [4 x ptr] [ptr inttoptr (i64 -16 to ptr), ptr null, ptr @_ZN5Base15func0Ev, ptr @_ZN5Base15func1Ev] }, !type !3, !type !4, !type !5, !type !6
+
+define i32 @testfunc(ptr %d) {
+entry:
+  %vtable = load ptr, ptr %d, !prof !7
+  %vfn = getelementptr inbounds ptr, ptr %vtable, i64 1
+  %0 = load ptr, ptr %vfn
+  %call = tail call i32 %0(ptr %d), !prof !8
+  ret i32 %call
+}
+
+define i32 @_ZN5Base15func1Ev(ptr %this) {
+entry:
+  ret i32 2
+}
+
+declare i32 @_ZN5Base25func2Ev(ptr)
+declare i32 @_ZN5Base15func0Ev(ptr)
+declare void @_ZN5Base35func3Ev(ptr)
+
+!0 = !{i64 16, !"_ZTS5Base1"}
+!1 = !{i64 48, !"_ZTS5Base2"}
+!2 = !{i64 16, !"_ZTS8Derived1"}
+!3 = !{i64 64, !"_ZTS5Base1"}
+!4 = !{i64 40, !"_ZTS5Base2"}
+!5 = !{i64 16, !"_ZTS5Base3"}
+!6 = !{i64 16, !"_ZTS8Derived2"}
+!7 = !{!"VP", i32 2, i64 1600, i64 -9064381665493407289, i64 800, i64 5035968517245772950, i64 500, i64 3215870116411581797, i64 300}
+!8 = !{!"VP", i32 0, i64 1600, i64 6804820478065511155, i64 1600})IR");
+
+  Function *F = M->getFunction("testfunc");
+  CallInst *CI = dyn_cast<CallInst>(&*std::next(F->front().rbegin()));
+  ASSERT_TRUE(CI && CI->isIndirectCall());
+
+  LoadInst *FuncPtr = dyn_cast<LoadInst>(CI->getCalledOperand());
+
+  GetElementPtrInst *GEP =
+      dyn_cast<GetElementPtrInst>(FuncPtr->getPointerOperand());
+
+  // Create the constant and the branch weights
+  SmallVector<Constant *, 3> VTableAddressPoints;
+
+  for (auto &[VTableName, AddressPointOffset] : {std::pair{"_ZTV5Base1", 16},
+                                                 {"_ZTV8Derived1", 16},
+                                                 {"_ZTV8Derived2", 64}})
+    VTableAddressPoints.push_back(getVTableAddressPointOffset(
+        M->getGlobalVariable(VTableName), AddressPointOffset));
+
+  MDBuilder MDB(C);
+  MDNode *BranchWeights = MDB.createBranchWeights(1600, 0);
+
+  size_t OrigEntryBBSize = F->front().size();
+
+  LoadInst *VPtr = dyn_cast<LoadInst>(&*F->front().begin());
+
+  Function *Callee = M->getFunction("_ZN5Base15func1Ev");
+  // Tests that promoted direct call is returned.
+  CallBase &DirectCB = promoteCallWithVTableCmp(
+      *CI, VPtr, Callee, VTableAddressPoints, BranchWeights);
+  EXPECT_EQ(DirectCB.getCalledOperand(), Callee);
+
+  // GEP and FuncPtr remains in the original block. `promoteCallWithVTableCmp`
----------------
david-xl wrote:

Is this required behavior? If yes, add a comment about it how later pass to sink them to the fallback branch.

https://github.com/llvm/llvm-project/pull/81378