Author: labath Date: Mon May 14 04:02:23 2018 New Revision: 332228 URL: http://llvm.org/viewvc/llvm-project?rev=332228&view=rev Log: [CodeGen] Disable aggressive structor optimizations at -O0
Summary: Removing the full structor and replacing all usages with the base one can degrade debug quality as it will leave the debugger unable to locate the full object structor. This is apparent when evaluating an expression in the debugger which requires constructing an object of class which has had this optimization applied to it. When compiling the expression, we pretend that the class and its methods have been defined in another compilation unit, so the expression compiler assumes the structor definition must be available. This didn't use to be the case for structors with internal linkage. Less aggressive optimizations like emitting the full structor as an alias remain in place, as they do not cause the structor symbol to disappear completely. This improves debug quality on non-darwin platforms (darwin does not have -mconstructor-aliases on by default, so it is spared these problems) and enable us to remove some workarounds from LLDB which attempt to mitigate this issue. Reviewers: rjmccall, aprantl Subscribers: cfe-commits Differential Revision: https://reviews.llvm.org/D46685 Modified: cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp cfe/trunk/test/CodeGenCXX/ctor-dtor-alias.cpp cfe/trunk/test/CodeGenCXX/float16-declarations.cpp Modified: cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp?rev=332228&r1=332227&r2=332228&view=diff ============================================================================== --- cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp (original) +++ cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp Mon May 14 04:02:23 2018 @@ -3630,12 +3630,16 @@ static StructorCodegen getCodegenToUse(C } llvm::GlobalValue::LinkageTypes Linkage = CGM.getFunctionLinkage(AliasDecl); - if (llvm::GlobalValue::isDiscardableIfUnused(Linkage)) - return StructorCodegen::RAUW; + // Only use RAUW in optimized code, as it makes the complete structor symbol + // disappear completely, which degrades debugging experience. + if (CGM.getCodeGenOpts().OptimizationLevel > 0) { + if (llvm::GlobalValue::isDiscardableIfUnused(Linkage)) + return StructorCodegen::RAUW; - // FIXME: Should we allow available_externally aliases? - if (!llvm::GlobalAlias::isValidLinkage(Linkage)) - return StructorCodegen::RAUW; + // FIXME: Should we allow available_externally aliases? + if (!llvm::GlobalAlias::isValidLinkage(Linkage)) + return StructorCodegen::RAUW; + } if (llvm::GlobalValue::isWeakForLinker(Linkage)) { // Only ELF and wasm support COMDATs with arbitrary names (C5/D5). Modified: cfe/trunk/test/CodeGenCXX/ctor-dtor-alias.cpp URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/ctor-dtor-alias.cpp?rev=332228&r1=332227&r2=332228&view=diff ============================================================================== --- cfe/trunk/test/CodeGenCXX/ctor-dtor-alias.cpp (original) +++ cfe/trunk/test/CodeGenCXX/ctor-dtor-alias.cpp Mon May 14 04:02:23 2018 @@ -77,11 +77,12 @@ namespace test4 { // CHECK1: call i32 @__cxa_atexit{{.*}}_ZN5test41AD2Ev // CHECK1: define linkonce_odr void @_ZN5test41AD2Ev({{.*}} comdat align - // test that we don't do this optimization at -O0 so that the debugger can - // see both destructors. + // test that we don't do this optimization at -O0 and call the complete + // destructor for B instead. This enables the debugger to see both + // destructors. + // NOOPT: @_ZN5test41BD1Ev = linkonce_odr alias void {{.*}} @_ZN5test41BD2Ev // NOOPT: define internal void @__cxx_global_var_init.2() - // NOOPT: call i32 @__cxa_atexit{{.*}}@_ZN5test41BD2Ev - // NOOPT: define linkonce_odr void @_ZN5test41BD2Ev({{.*}} comdat align + // NOOPT: call i32 @__cxa_atexit{{.*}}@_ZN5test41BD1Ev struct A { virtual ~A() {} }; Modified: cfe/trunk/test/CodeGenCXX/float16-declarations.cpp URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/float16-declarations.cpp?rev=332228&r1=332227&r2=332228&view=diff ============================================================================== --- cfe/trunk/test/CodeGenCXX/float16-declarations.cpp (original) +++ cfe/trunk/test/CodeGenCXX/float16-declarations.cpp Mon May 14 04:02:23 2018 @@ -103,7 +103,7 @@ int main(void) { C1 c1(f1l); // CHECK-DAG: [[F1L:%[a-z0-9]+]] = load half, half* %{{.*}}, align 2 -// CHECK-DAG: call void @_ZN2C1C2EDF16_(%class.C1* %{{.*}}, half %{{.*}}) +// CHECK-DAG: call void @_ZN2C1C1EDF16_(%class.C1* %{{.*}}, half %{{.*}}) S1<_Float16> s1 = { 132.f16 }; // CHECK-DAG: @_ZZ4mainE2s1 = private unnamed_addr constant %struct.S1 { half 0xH5820 }, align 2 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
