I added !invariant.load to virtual functions load, so when optimizer see case like this
%vtable = load ... %1 = load (...) %vtable, !invariant.load !0 call %1(...) %2 = load (...) %vtable, !invariant.load !0 call %2(...) can merge the 2 virtual functions load into one like this: %vtable = load ... %1 = load (...) %vtable, !invariant.load !0 call %1(...) call %1(...) This change requires -fstrict-vtable-pointers because without !invariant.group optimizer will not merge vtable load into one load, and because of it !invariant.load will be useless. On Wed, Sep 30, 2015 at 9:28 PM, Chandler Carruth <chandl...@gmail.com> wrote: > On Wed, Sep 30, 2015 at 8:52 PM Piotr Padlewski via cfe-commits < > cfe-commits@lists.llvm.org> wrote: > >> Author: prazek >> Date: Wed Sep 30 22:50:41 2015 >> New Revision: 248982 >> >> URL: http://llvm.org/viewvc/llvm-project?rev=248982&view=rev >> Log: >> Decorating virtual functions load with invariant.load >> > > This change description really doesn't tell me anything about what this > change does. Could you try to write more detailed and explanatory change > logs? > > Imagine a reader that has little or no context reading the change log to > gain the context necessary to read the actual patch and understand what is > going on with it. > > >> >> http://reviews.llvm.org/D13279 >> >> Modified: >> cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp >> cfe/trunk/test/CodeGenCXX/virtual-function-calls.cpp >> >> Modified: cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp >> URL: >> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp?rev=248982&r1=248981&r2=248982&view=diff >> >> ============================================================================== >> --- cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp (original) >> +++ cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp Wed Sep 30 22:50:41 2015 >> @@ -1609,7 +1609,16 @@ llvm::Value *ItaniumCXXABI::getVirtualFu >> uint64_t VTableIndex = >> CGM.getItaniumVTableContext().getMethodVTableIndex(GD); >> llvm::Value *VFuncPtr = >> CGF.Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfn"); >> - return CGF.Builder.CreateAlignedLoad(VFuncPtr, CGF.getPointerAlign()); >> + auto *Inst = CGF.Builder.CreateAlignedLoad(VFuncPtr, >> CGF.getPointerAlign()); >> + >> + // It's safe to add "invariant.load" without -fstrict-vtable-pointers, >> but it >> + // would not help in devirtualization. >> + if (CGM.getCodeGenOpts().OptimizationLevel > 0 && >> + CGM.getCodeGenOpts().StrictVTablePointers) >> + Inst->setMetadata(llvm::LLVMContext::MD_invariant_load, >> + llvm::MDNode::get(CGM.getLLVMContext(), >> + llvm::ArrayRef<llvm::Metadata >> *>())); >> + return Inst; >> } >> >> llvm::Value *ItaniumCXXABI::EmitVirtualDestructorCall( >> >> Modified: cfe/trunk/test/CodeGenCXX/virtual-function-calls.cpp >> URL: >> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/virtual-function-calls.cpp?rev=248982&r1=248981&r2=248982&view=diff >> >> ============================================================================== >> --- cfe/trunk/test/CodeGenCXX/virtual-function-calls.cpp (original) >> +++ cfe/trunk/test/CodeGenCXX/virtual-function-calls.cpp Wed Sep 30 >> 22:50:41 2015 >> @@ -1,4 +1,5 @@ >> // RUN: %clang_cc1 %s -triple %itanium_abi_triple -std=c++11 -emit-llvm >> -o - | FileCheck %s >> +// RUN: %clang_cc1 %s -triple %itanium_abi_triple -std=c++11 -emit-llvm >> -o - -fstrict-vtable-pointers -O1 | FileCheck >> --check-prefix=CHECK-INVARIANT %s >> >> // PR5021 >> namespace PR5021 { >> @@ -42,10 +43,14 @@ namespace VirtualNoreturn { >> [[noreturn]] virtual void f(); >> }; >> >> - // CHECK: @_ZN15VirtualNoreturn1f >> + // CHECK-LABEL: @_ZN15VirtualNoreturn1f >> + // CHECK-INVARIANT-LABEL: define void @_ZN15VirtualNoreturn1f >> void f(A *p) { >> p->f(); >> // CHECK: call {{.*}}void %{{[^#]*$}} >> // CHECK-NOT: unreachable >> + // CHECK-INVARIANT: load {{.*}} align 8, !invariant.load >> ![[EMPTY_NODE:[0-9]]] >> } >> } >> + >> +// CHECK-INVARIANT: ![[EMPTY_NODE]] = !{} >> >> >> _______________________________________________ >> cfe-commits mailing list >> cfe-commits@lists.llvm.org >> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits >> >
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