arphaman updated this revision to Diff 81584.
arphaman marked 3 inline comments as done.
arphaman added a comment.
The updated patch removes the dependency on the "-Wreturn-type" diagnostic and
verifies that functions that return a type with a non-trivial default
constructor are always optimized.
Repository:
rL LLVM
https://reviews.llvm.org/D27163
Files:
include/clang/Driver/Options.td
include/clang/Frontend/CodeGenOptions.def
lib/CodeGen/CodeGenFunction.cpp
lib/Driver/Tools.cpp
lib/Frontend/CompilerInvocation.cpp
test/CodeGenCXX/return.cpp
test/CodeGenObjCXX/return.mm
test/Driver/clang_f_opts.c
Index: test/Driver/clang_f_opts.c
===================================================================
--- test/Driver/clang_f_opts.c
+++ test/Driver/clang_f_opts.c
@@ -469,3 +469,8 @@
// CHECK-WCHAR2: -fshort-wchar
// CHECK-WCHAR2-NOT: -fno-short-wchar
// DELIMITERS: {{^ *"}}
+
+// RUN: %clang -### -S -fstrict-return %s 2>&1 | FileCheck -check-prefix=CHECK-STRICT-RETURN %s
+// RUN: %clang -### -S -fno-strict-return %s 2>&1 | FileCheck -check-prefix=CHECK-NO-STRICT-RETURN %s
+// CHECK-STRICT-RETURN-NOT: "-fno-strict-return"
+// CHECK-NO-STRICT-RETURN: "-fno-strict-return"
Index: test/CodeGenObjCXX/return.mm
===================================================================
--- /dev/null
+++ test/CodeGenObjCXX/return.mm
@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -emit-llvm -fblocks -triple x86_64-apple-darwin -fstrict-return -o - %s | FileCheck %s
+// RUN: %clang_cc1 -emit-llvm -fblocks -triple x86_64-apple-darwin -fstrict-return -O -o - %s | FileCheck %s
+
+@interface I
+@end
+
+@implementation I
+
+- (int)method {
+}
+
+@end
+
+enum Enum {
+ a
+};
+
+int (^block)(Enum) = ^int(Enum e) {
+ switch (e) {
+ case a:
+ return 1;
+ }
+};
+
+// Ensure that both methods and blocks don't use the -fstrict-return undefined
+// behaviour optimization.
+
+// CHECK-NOT: call void @llvm.trap
+// CHECK-NOT: unreachable
Index: test/CodeGenCXX/return.cpp
===================================================================
--- test/CodeGenCXX/return.cpp
+++ test/CodeGenCXX/return.cpp
@@ -1,12 +1,105 @@
-// RUN: %clang_cc1 -emit-llvm -triple %itanium_abi_triple -o - %s | FileCheck %s
-// RUN: %clang_cc1 -emit-llvm -triple %itanium_abi_triple -O -o - %s | FileCheck %s --check-prefix=CHECK-OPT
+// RUN: %clang_cc1 -emit-llvm -triple %itanium_abi_triple -std=c++11 -o - %s | FileCheck --check-prefixes=CHECK,CHECK-COMMON %s
+// RUN: %clang_cc1 -emit-llvm -triple %itanium_abi_triple -std=c++11 -O -o - %s | FileCheck %s --check-prefixes=CHECK-OPT,CHECK-COMMON
+// RUN: %clang_cc1 -emit-llvm -triple %itanium_abi_triple -std=c++11 -fno-strict-return -o - %s | FileCheck %s --check-prefixes=CHECK-NOSTRICT,CHECK-COMMON
+// RUN: %clang_cc1 -emit-llvm -triple %itanium_abi_triple -std=c++11 -fno-strict-return -Wno-return-type -o - %s | FileCheck %s --check-prefixes=CHECK-NOSTRICT,CHECK-COMMON
+// RUN: %clang_cc1 -emit-llvm -triple %itanium_abi_triple -std=c++11 -fno-strict-return -O -o - %s | FileCheck %s --check-prefixes=CHECK-NOSTRICT-OPT,CHECK-COMMON
-// CHECK: @_Z9no_return
-// CHECK-OPT: @_Z9no_return
+// CHECK-COMMON-LABEL: @_Z9no_return
int no_return() {
// CHECK: call void @llvm.trap
// CHECK-NEXT: unreachable
// CHECK-OPT-NOT: call void @llvm.trap
// CHECK-OPT: unreachable
+
+ // -fno-strict-return should not emit trap + unreachable but it should return
+ // an undefined value instead.
+
+ // CHECK-NOSTRICT: entry:
+ // CHECK-NOSTRICT-NEXT: alloca
+ // CHECK-NOSTRICT-NEXT: load
+ // CHECK-NOSTRICT-NEXT: ret i32
+ // CHECK-NOSTRICT-NEXT: }
+
+ // CHECK-NOSTRICT-OPT: entry:
+ // CHECK-NOSTRICT-OPT: ret i32 undef
+}
+
+enum Enum {
+ A, B
+};
+
+// CHECK-COMMON-LABEL: @_Z27returnNotViableDontOptimize4Enum
+int returnNotViableDontOptimize(Enum e) {
+ switch (e) {
+ case A: return 1;
+ case B: return 2;
+ }
+ // Undefined behaviour optimization shouldn't be used when -fno-strict-return
+ // is turned on, even if all the enum cases are covered in this function.
+
+ // CHECK-NOSTRICT-NOT: call void @llvm.trap
+ // CHECK-NOSTRICT-NOT: unreachable
+}
+
+struct Trivial {
+ int x;
+};
+
+// CHECK-NOSTRICT-LABEL: @_Z7trivialv
+Trivial trivial() {
+ // This function returns a trivial record so -fno-strict-return should avoid
+ // the undefined behaviour optimization.
+
+ // CHECK-NOSTRICT-NOT: call void @llvm.trap
+ // CHECK-NOSTRICT-NOT: unreachable
+}
+
+// Functions that return non-trivial records should always use the
+// -fstrict-return optimization.
+
+struct NonTrivialCopy {
+ NonTrivialCopy(const NonTrivialCopy &);
+};
+
+// CHECK-NOSTRICT-LABEL: @_Z14nonTrivialCopyv
+NonTrivialCopy nonTrivialCopy() {
+ // CHECK-NOSTRICT: call void @llvm.trap
+ // CHECK-NOSTRICT-NEXT: unreachable
+}
+
+struct NonTrivialDestructor {
+ ~NonTrivialDestructor();
+};
+
+// CHECK-NOSTRICT-LABEL: @_Z20nonTrivialDestructorv
+NonTrivialDestructor nonTrivialDestructor() {
+ // CHECK-NOSTRICT: call void @llvm.trap
+ // CHECK-NOSTRICT-NEXT: unreachable
+}
+
+// The behavior for lambdas should be identical to functions.
+// CHECK-COMMON-LABEL: @_Z10lambdaTestv
+void lambdaTest() {
+ auto lambda1 = []() -> int {
+ };
+ lambda1();
+
+ // CHECK: call void @llvm.trap
+ // CHECK-NEXT: unreachable
+
+ // CHECK-NOSTRICT-NOT: call void @llvm.trap
+ // CHECK-NOSTRICT-NOT: unreachable
+}
+
+struct NonTrivialDefaultConstructor {
+ int x;
+
+ NonTrivialDefaultConstructor() { }
+};
+
+// CHECK-NOSTRICT-LABEL: @_Z28nonTrivialDefaultConstructorv
+NonTrivialDefaultConstructor nonTrivialDefaultConstructor() {
+ // CHECK-NOSTRICT: call void @llvm.trap
+ // CHECK-NOSTRICT-NEXT: unreachable
}
Index: lib/Frontend/CompilerInvocation.cpp
===================================================================
--- lib/Frontend/CompilerInvocation.cpp
+++ lib/Frontend/CompilerInvocation.cpp
@@ -596,6 +596,7 @@
Opts.NoDwarfDirectoryAsm = Args.hasArg(OPT_fno_dwarf_directory_asm);
Opts.SoftFloat = Args.hasArg(OPT_msoft_float);
Opts.StrictEnums = Args.hasArg(OPT_fstrict_enums);
+ Opts.StrictReturn = !Args.hasArg(OPT_fno_strict_return);
Opts.StrictVTablePointers = Args.hasArg(OPT_fstrict_vtable_pointers);
Opts.UnsafeFPMath = Args.hasArg(OPT_menable_unsafe_fp_math) ||
Args.hasArg(OPT_cl_unsafe_math_optimizations) ||
Index: lib/Driver/Tools.cpp
===================================================================
--- lib/Driver/Tools.cpp
+++ lib/Driver/Tools.cpp
@@ -4437,6 +4437,9 @@
if (Args.hasFlag(options::OPT_fstrict_enums, options::OPT_fno_strict_enums,
false))
CmdArgs.push_back("-fstrict-enums");
+ if (!Args.hasFlag(options::OPT_fstrict_return, options::OPT_fno_strict_return,
+ true))
+ CmdArgs.push_back("-fno-strict-return");
if (Args.hasFlag(options::OPT_fstrict_vtable_pointers,
options::OPT_fno_strict_vtable_pointers,
false))
Index: lib/CodeGen/CodeGenFunction.cpp
===================================================================
--- lib/CodeGen/CodeGenFunction.cpp
+++ lib/CodeGen/CodeGenFunction.cpp
@@ -1067,6 +1067,25 @@
return ResTy;
}
+/// Return true if the given function \p FD should use the undefined behavior
+/// return optimization.
+static bool
+shouldUseUndefinedBehaviorReturnOptimization(const FunctionDecl *FD,
+ const ASTContext &Context) {
+ QualType T = FD->getReturnType();
+ if (T.isTriviallyCopyableType(Context)) {
+ // Avoid the optimization for functions that return trivially copyable
+ // types with a trivial destructor and a trivial default constructor.
+ if (const RecordType *RT = T.getCanonicalType()->getAs<RecordType>()) {
+ if (const CXXRecordDecl *ClassDecl =
+ dyn_cast<CXXRecordDecl>(RT->getDecl()))
+ return ClassDecl->hasNonTrivialDefaultConstructor();
+ }
+ return false;
+ }
+ return true;
+}
+
void CodeGenFunction::GenerateCode(GlobalDecl GD, llvm::Function *Fn,
const CGFunctionInfo &FnInfo) {
const FunctionDecl *FD = cast<FunctionDecl>(GD.getDecl());
@@ -1145,17 +1164,23 @@
// function call is used by the caller, the behavior is undefined.
if (getLangOpts().CPlusPlus && !FD->hasImplicitReturnZero() && !SawAsmBlock &&
!FD->getReturnType()->isVoidType() && Builder.GetInsertBlock()) {
+ bool ShouldEmitUnreachable =
+ CGM.getCodeGenOpts().StrictReturn ||
+ shouldUseUndefinedBehaviorReturnOptimization(FD, getContext());
if (SanOpts.has(SanitizerKind::Return)) {
SanitizerScope SanScope(this);
llvm::Value *IsFalse = Builder.getFalse();
EmitCheck(std::make_pair(IsFalse, SanitizerKind::Return),
SanitizerHandler::MissingReturn,
EmitCheckSourceLocation(FD->getLocation()), None);
- } else if (CGM.getCodeGenOpts().OptimizationLevel == 0) {
- EmitTrapCall(llvm::Intrinsic::trap);
+ } else if (ShouldEmitUnreachable) {
+ if (CGM.getCodeGenOpts().OptimizationLevel == 0)
+ EmitTrapCall(llvm::Intrinsic::trap);
+ }
+ if (SanOpts.has(SanitizerKind::Return) || ShouldEmitUnreachable) {
+ Builder.CreateUnreachable();
+ Builder.ClearInsertionPoint();
}
- Builder.CreateUnreachable();
- Builder.ClearInsertionPoint();
}
// Emit the standard function epilogue.
Index: include/clang/Frontend/CodeGenOptions.def
===================================================================
--- include/clang/Frontend/CodeGenOptions.def
+++ include/clang/Frontend/CodeGenOptions.def
@@ -255,6 +255,10 @@
/// Whether copy relocations support is available when building as PIE.
CODEGENOPT(PIECopyRelocations, 1, 0)
+/// Whether we should use the undefined behaviour optimization for control flow
+/// paths that reach the end of a function without executing a required return.
+CODEGENOPT(StrictReturn, 1, 1)
+
#undef CODEGENOPT
#undef ENUM_CODEGENOPT
#undef VALUE_CODEGENOPT
Index: include/clang/Driver/Options.td
===================================================================
--- include/clang/Driver/Options.td
+++ include/clang/Driver/Options.td
@@ -1318,6 +1318,12 @@
def fno_unique_section_names : Flag <["-"], "fno-unique-section-names">,
Group<f_Group>, Flags<[CC1Option]>;
+def fstrict_return : Flag<["-"], "fstrict-return">, Group<f_Group>,
+ Flags<[CC1Option]>,
+ HelpText<"Use C++ undefined behaviour optimization for control flow paths"
+ "that reach the end of the function without executing a required return">;
+def fno_strict_return : Flag<["-"], "fno-strict-return">, Group<f_Group>,
+ Flags<[CC1Option]>;
def fdebug_types_section: Flag <["-"], "fdebug-types-section">, Group<f_Group>,
Flags<[CC1Option]>, HelpText<"Place debug types in their own section (ELF Only)">;
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