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[clang][PAC] Enable the PAC dynamic_cast to final class optimization
Update the codegen for the the dynamic_cast to a final class optimization when pointer authentication is enabled.
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5 files changed

+170
-3
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5 files changed

+170
-3
lines changed

‎clang/docs/ReleaseNotes.rst

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Original file line numberDiff line numberDiff line change
@@ -184,6 +184,8 @@ Bug Fixes to C++ Support
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(``[[assume(expr)]]``) creates temporary objects.
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- Fix the dynamic_cast to final class optimization to correctly handle
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casts that are guaranteed to fail (#GH137518).
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- Support the dynamic_cast to final class optimization with pointer
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authentication enabled.
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Bug Fixes to AST Handling
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^^^^^^^^^^^^^^^^^^^^^^^^^

‎clang/lib/CodeGen/CGExprCXX.cpp

Lines changed: 1 addition & 2 deletions
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@@ -2292,8 +2292,7 @@ llvm::Value *CodeGenFunction::EmitDynamicCast(Address ThisAddr,
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bool IsExact = !IsDynamicCastToVoid &&
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CGM.getCodeGenOpts().OptimizationLevel > 0 &&
22942294
DestRecordTy->getAsCXXRecordDecl()->isEffectivelyFinal() &&
2295-
CGM.getCXXABI().shouldEmitExactDynamicCast(DestRecordTy) &&
2296-
!getLangOpts().PointerAuthCalls;
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CGM.getCXXABI().shouldEmitExactDynamicCast(DestRecordTy);
22972296

22982297
std::optional<CGCXXABI::ExactDynamicCastInfo> ExactCastInfo;
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if (IsExact) {

‎clang/lib/CodeGen/ItaniumCXXABI.cpp

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@@ -1745,7 +1745,14 @@ llvm::Value *ItaniumCXXABI::emitExactDynamicCast(
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llvm::BasicBlock *CastFail) {
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const CXXRecordDecl *SrcDecl = SrcRecordTy->getAsCXXRecordDecl();
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const CXXRecordDecl *DestDecl = DestRecordTy->getAsCXXRecordDecl();
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auto AuthenticateVTable = [&](Address ThisAddr, const CXXRecordDecl *Decl) {
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if (!CGF.getLangOpts().PointerAuthCalls)
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return;
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(void)CGF.GetVTablePtr(ThisAddr, CGF.UnqualPtrTy, Decl,
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CodeGenFunction::VTableAuthMode::MustTrap);
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};
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bool PerformPostCastAuthentication = false;
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llvm::Value *VTable = nullptr;
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if (ExactCastInfo.RequiresCastToPrimaryBase) {
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// Base appears in at least two different places. Find the most-derived
@@ -1756,8 +1763,16 @@ llvm::Value *ItaniumCXXABI::emitExactDynamicCast(
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emitDynamicCastToVoid(CGF, ThisAddr, SrcRecordTy);
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ThisAddr = Address(PrimaryBase, CGF.VoidPtrTy, ThisAddr.getAlignment());
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SrcDecl = DestDecl;
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// This unauthenticated load is unavoidable, so we're relying on the
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// authenticated load in the dynamic cast to void, and we'll manually
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// authenticate the resulting v-table at the end of the cast check.
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PerformPostCastAuthentication = CGF.getLangOpts().PointerAuthCalls;
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CGPointerAuthInfo StrippingAuthInfo(0, PointerAuthenticationMode::Strip,
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false, false, nullptr);
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Address VTablePtrPtr = ThisAddr.withElementType(CGF.VoidPtrPtrTy);
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VTable = CGF.Builder.CreateLoad(VTablePtrPtr, "vtable");
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if (PerformPostCastAuthentication)
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VTable = CGF.EmitPointerAuthAuth(StrippingAuthInfo, VTable);
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} else
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VTable = CGF.GetVTablePtr(ThisAddr, CGF.UnqualPtrTy, SrcDecl);
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@@ -1774,8 +1789,32 @@ llvm::Value *ItaniumCXXABI::emitExactDynamicCast(
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llvm::ConstantInt::get(CGF.PtrDiffTy, -Offset);
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AdjustedThisPtr = CGF.Builder.CreateInBoundsGEP(CGF.CharTy, AdjustedThisPtr,
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OffsetConstant);
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PerformPostCastAuthentication = CGF.getLangOpts().PointerAuthCalls;
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}
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if (PerformPostCastAuthentication) {
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// If we've changed the object pointer we authenticate the vtable pointer
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// of the resulting object.
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llvm::BasicBlock *NonNullBlock = CGF.Builder.GetInsertBlock();
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llvm::BasicBlock *PostCastAuthSuccess =
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CGF.createBasicBlock("dynamic_cast.postauth.success");
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llvm::BasicBlock *PostCastAuthComplete =
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CGF.createBasicBlock("dynamic_cast.postauth.complete");
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CGF.Builder.CreateCondBr(Success, PostCastAuthSuccess,
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PostCastAuthComplete);
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CGF.EmitBlock(PostCastAuthSuccess);
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Address AdjustedThisAddr =
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Address(AdjustedThisPtr, CGF.IntPtrTy, CGF.getPointerAlign());
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AuthenticateVTable(AdjustedThisAddr, DestDecl);
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CGF.EmitBranch(PostCastAuthComplete);
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CGF.EmitBlock(PostCastAuthComplete);
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llvm::PHINode *PHI = CGF.Builder.CreatePHI(AdjustedThisPtr->getType(), 2);
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PHI->addIncoming(AdjustedThisPtr, PostCastAuthSuccess);
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llvm::Value *NullValue =
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llvm::Constant::getNullValue(AdjustedThisPtr->getType());
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PHI->addIncoming(NullValue, NonNullBlock);
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AdjustedThisPtr = PHI;
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}
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CGF.Builder.CreateCondBr(Success, CastSuccess, CastFail);
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return AdjustedThisPtr;
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}

‎clang/test/CodeGenCXX/dynamic-cast-exact-disabled.cpp

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@@ -3,7 +3,6 @@
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// RUN: %clang_cc1 -I%S %s -triple x86_64-apple-darwin10 -O1 -fvisibility=hidden -emit-llvm -std=c++11 -o - | FileCheck %s --check-prefixes=CHECK,INEXACT
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// RUN: %clang_cc1 -I%S %s -triple x86_64-apple-darwin10 -O1 -fapple-kext -emit-llvm -std=c++11 -o - | FileCheck %s --check-prefixes=CHECK,INEXACT
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// RUN: %clang_cc1 -I%S %s -triple x86_64-apple-darwin10 -O1 -fno-assume-unique-vtables -emit-llvm -std=c++11 -o - | FileCheck %s --check-prefixes=CHECK,INEXACT
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// RUN: %clang_cc1 -I%S %s -triple arm64e-apple-darwin10 -O1 -fptrauth-calls -emit-llvm -std=c++11 -o - | FileCheck %s --check-prefixes=CHECK,INEXACT
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struct A { virtual ~A(); };
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struct B final : A { };

‎clang/test/CodeGenCXX/ptrauth-dynamic-cast-exact.cpp

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@@ -0,0 +1,128 @@
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// RUN: %clang_cc1 -I%S %s -triple arm64e-apple-darwin10 -O1 -fptrauth-calls -fptrauth-vtable-pointer-address-discrimination -fptrauth-vtable-pointer-type-discrimination -emit-llvm -std=c++11 -o - | FileCheck %s --check-prefixes=CHECK
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struct A {
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virtual ~A();
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};
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struct B {
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int foo;
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virtual ~B();
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};
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struct C final : A, B {
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virtual void f(){};
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};
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struct D final : B, A {
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virtual void f(){};
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};
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struct Offset {
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virtual ~Offset();
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};
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struct E {
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virtual ~E();
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};
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struct F final : Offset, E {
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};
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struct G {
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virtual ~G();
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int g;
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};
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struct H : E {
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int h;
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};
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struct I : E {
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int i;
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};
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struct J : virtual E {
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int j;
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};
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struct K : virtual E {
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int k;
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};
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struct L final : G, H, I, J, K {
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int l;
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};
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struct M final: G, private H { int m; };
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// CHECK-LABEL: @_Z10exact_to_CP1A
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C *exact_to_C(A *a) {
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// CHECK: [[UNAUTHED_VPTR:%.*]] = load ptr, ptr %a, align 8
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// CHECK: [[VPTR_ADDRI:%.*]] = ptrtoint ptr %a to i64
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// CHECK: [[VPTR_ADDR_DISC:%.*]] = tail call i64 @llvm.ptrauth.blend(i64 [[VPTR_ADDRI]], i64 62866)
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// CHECK: [[UNAUTHED_VPTRI:%.*]] = ptrtoint ptr [[UNAUTHED_VPTR]] to i64
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// CHECK: [[AUTHED_VPTRI:%.*]] = tail call i64 @llvm.ptrauth.auth(i64 [[UNAUTHED_VPTRI]], i32 2, i64 [[VPTR_ADDR_DISC]])
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// CHECK: [[IS_EXPECTED:%.*]] = icmp eq i64 [[AUTHED_VPTRI]], ptrtoint (ptr getelementptr inbounds nuw inrange(-16, 24) (i8, ptr @_ZTV1C, i64 16) to i64)
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// CHECK: br i1 [[IS_EXPECTED]], label %dynamic_cast.end, label %dynamic_cast.null
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// CHECK: [[NULL_CHECKED_RESULT:%.*]] = phi ptr [ %a, %dynamic_cast.notnull ], [ null, %dynamic_cast.null ]
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// CHECK: ret ptr [[NULL_CHECKED_RESULT]]
57+
return dynamic_cast<C*>(a);
58+
}
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60+
// CHECK-LABEL: @_Z9exact_t_DP1A
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D *exact_t_D(A *a) {
62+
// CHECK: dynamic_cast.notnull:
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// CHECK: [[SRC_UNAUTHED_VPTR:%.*]] = load ptr, ptr %a
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// CHECK: [[SRC_VPTR_ADDRI:%.*]] = ptrtoint ptr %a to i64
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// CHECK: [[SRC_VPTR_DISC:%.*]] = tail call i64 @llvm.ptrauth.blend(i64 [[SRC_VPTR_ADDRI]], i64 62866)
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// CHECK: [[SRC_UNAUTHED_VPTRI:%.*]] = ptrtoint ptr [[SRC_UNAUTHED_VPTR]] to i64
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// CHECK: [[SRC_AUTHED_VPTRI:%.*]] = tail call i64 @llvm.ptrauth.auth(i64 [[SRC_UNAUTHED_VPTRI]], i32 2, i64 [[SRC_VPTR_DISC]])
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// CHECK: [[SUCCESS:%.*]] = icmp eq i64 [[SRC_AUTHED_VPTRI]], ptrtoint (ptr getelementptr inbounds nuw inrange(-16, 16) (i8, ptr @_ZTV1D, i64 56) to i64)
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// CHECK: br i1 [[SUCCESS]], label %dynamic_cast.postauth.success, label %dynamic_cast.postauth.complete
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// CHECK: dynamic_cast.postauth.success:
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// CHECK: [[ADJUSTED_THIS:%.*]] = getelementptr inbounds i8, ptr %a, i64 -16
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// CHECK: [[ADJUSTED_UNAUTHED_VPTR:%.*]] = load ptr, ptr [[ADJUSTED_THIS]]
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// CHECK: [[ADJUSTED_VPTR_ADDRI:%.*]] = ptrtoint ptr [[ADJUSTED_THIS]] to i64
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// CHECK: [[ADJUSTED_VPTR_DISC:%.*]] = tail call i64 @llvm.ptrauth.blend(i64 [[ADJUSTED_VPTR_ADDRI]], i64 28965)
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// CHECK: [[ADJUSTED_UNAUTHED_VPTRI:%.*]] = ptrtoint ptr [[ADJUSTED_UNAUTHED_VPTR]] to i64
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// CHECK: [[ADJUSTED_AUTHED_VPTRI:%.*]] = tail call i64 @llvm.ptrauth.auth(i64 [[ADJUSTED_UNAUTHED_VPTRI]], i32 2, i64 [[ADJUSTED_VPTR_DISC]])
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// CHECK: [[ADJUSTED_AUTHED_VPTR:%.*]] = inttoptr i64 [[ADJUSTED_AUTHED_VPTRI]] to ptr
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// CHECK: br label %dynamic_cast.postauth.complete
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// CHECK: dynamic_cast.postauth.complete:
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// CHECK: [[AUTHED_ADJUSTED_THIS:%.*]] = phi ptr [ [[ADJUSTED_THIS]], %dynamic_cast.postauth.success ], [ null, %dynamic_cast.notnull ]
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// CHECK: br i1 [[SUCCESS]], label %dynamic_cast.end, label %dynamic_cast.null
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// CHECK: dynamic_cast.null:
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// CHECK: br label %dynamic_cast.end
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// CHECK: dynamic_cast.end:
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// CHECK: [[RESULT:%.*]] = phi ptr [ [[AUTHED_ADJUSTED_THIS]], %dynamic_cast.postauth.complete ], [ null, %dynamic_cast.null ]
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// CHECK: ret ptr [[RESULT]]
87+
return dynamic_cast<D*>(a);
88+
}
89+
90+
// CHECK-LABEL: @_Z11exact_multiP1E
91+
L *exact_multi(E *e) {
92+
// CHECK: dynamic_cast.notnull:
93+
// CHECK: [[VTABLE_ADDR:%.*]] = load ptr, ptr %e, align 8
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// CHECK: [[THIS_ADDRI:%.*]] = ptrtoint ptr %e to i64
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// CHECK: [[VTABLE_DISC:%.*]] = tail call i64 @llvm.ptrauth.blend(i64 [[THIS_ADDRI]], i64 12810)
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// CHECK: [[VTABLE_ADDRI:%.*]] = ptrtoint ptr [[VTABLE_ADDR]] to i64
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// CHECK: [[AUTHED_VTABLEI:%.*]] = tail call i64 @llvm.ptrauth.auth(i64 [[VTABLE_ADDRI]], i32 2, i64 [[VTABLE_DISC]])
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// CHECK: [[AUTHED_VTABLE:%.*]] = inttoptr i64 [[AUTHED_VTABLEI]] to ptr
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// CHECK: [[PRIMARY_BASE_OFFSET:%.*]] = getelementptr inbounds i8, ptr [[AUTHED_VTABLE]], i64 -16
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// CHECK: %offset.to.top = load i64, ptr [[PRIMARY_BASE_OFFSET]]
101+
// CHECK: [[ADJUSTED_THIS:%.*]] = getelementptr inbounds i8, ptr %e, i64 %offset.to.top
102+
// CHECK: [[ADJUSTED_THIS_VTABLE:%.*]] = load ptr, ptr [[ADJUSTED_THIS]]
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// CHECK: [[ADJUSTED_THIS_VTABLEI:%.*]] = ptrtoint ptr [[ADJUSTED_THIS_VTABLE]] to i64
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// CHECK: [[ADJUSTED_THIS_STRIPPED_VTABLEI:%.*]] = tail call i64 @llvm.ptrauth.strip(i64 [[ADJUSTED_THIS_VTABLEI]], i32 0)
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// CHECK: [[SUCCESS:%.*]] = icmp eq i64 [[ADJUSTED_THIS_STRIPPED_VTABLEI]], ptrtoint (ptr getelementptr inbounds nuw inrange(-24, 16) (i8, ptr @_ZTV1L, i64 24) to i64)
106+
// CHECK: br i1 [[SUCCESS]], label %dynamic_cast.postauth.success, label %dynamic_cast.postauth.complete
107+
// CHECK: dynamic_cast.postauth.success:
108+
// CHECK: [[ADJUSTED_THISI:%.*]] = ptrtoint ptr [[ADJUSTED_THIS]] to i64
109+
// CHECK: [[DEST_DISC:%.*]] = tail call i64 @llvm.ptrauth.blend(i64 [[ADJUSTED_THISI]], i64 41434)
110+
// CHECK: tail call i64 @llvm.ptrauth.auth(i64 [[ADJUSTED_THIS_VTABLEI]], i32 2, i64 [[DEST_DISC]])
111+
// CHECK: br label %dynamic_cast.postauth.complete
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// CHECK: dynamic_cast.postauth.complete:
113+
// CHECK: [[AUTHED_ADJUSTED_THIS:%.*]] = phi ptr [ [[ADJUSTED_THIS]], %dynamic_cast.postauth.success ], [ null, %dynamic_cast.notnull ]
114+
// CHECK: br i1 [[SUCCESS]], label %dynamic_cast.end, label %dynamic_cast.null
115+
// CHECK: dynamic_cast.null:
116+
// CHECK: br label %dynamic_cast.end
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// CHECK: dynamic_cast.end:
118+
// CHECK: [[RESULT:%.*]] = phi ptr [ [[AUTHED_ADJUSTED_THIS]], %dynamic_cast.postauth.complete ], [ null, %dynamic_cast.null ]
119+
// CHECK: ret ptr [[RESULT]]
120+
return dynamic_cast<L*>(e);
121+
}
122+
123+
// CHECK-LABEL: @_Z19exact_invalid_multiP1H
124+
M *exact_invalid_multi(H* d) {
125+
// CHECK: entry:
126+
// CHECK-NEXT: ret ptr null
127+
return dynamic_cast<M*>(d);
128+
}

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