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[Clang] Enable -fpointer-tbaa by default.
Support for more precise TBAA metadata has been added a while ago (behind the -fpointer-tbaa flag). The more precise TBAA metadata allows treating accesses of different pointer types as no-alias. This helps to remove more redundant loads and stores in a number of workloads. Some highlights on the impact across llvm-test-suite's MultiSource, SPEC2006 & SPEC2017 include: * +2% more NoAlias results for memory access * +4% more loops vectorized * +3% more stores removed by DSE. This closes a relatively big gap to GCC, which has been supporting disambiguating based on pointer types for a long time. (https://clang.godbolt.org/z/K7Wbhrz4q) Pointer-TBAA support for pointers to builtin types has been added in #76612. Support for user-defined types has been added in #110569. There are 2 pending PRs with bug fixes for special cases uncovered during some of my testing: * #116991 * #116596
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‎clang/docs/ReleaseNotes.rst

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@@ -211,6 +211,10 @@ C++ Language Changes
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- The builtin type alias ``__builtin_common_type`` has been added to improve the
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performance of ``std::common_type``.
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- Clang now emits distinct type-based alias analysis tags for incompatible
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pointers by default, enabling more powerful alias analysis when accessing
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pointer types. The new default behavior can be disabled using ``-fno-pointer-tbaa``.
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C++2c Feature Support
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^^^^^^^^^^^^^^^^^^^^^
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‎clang/include/clang/Basic/CodeGenOptions.def

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@@ -242,7 +242,7 @@ ENUM_CODEGENOPT(StructReturnConvention, StructReturnConventionKind, 2, SRCK_Defa
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CODEGENOPT(RelaxAll , 1, 0) ///< Relax all machine code instructions.
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CODEGENOPT(RelaxedAliasing , 1, 0) ///< Set when -fno-strict-aliasing is enabled.
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CODEGENOPT(PointerTBAA, 1, 0) ///< Whether or not to use distinct TBAA tags for pointers.
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CODEGENOPT(PointerTBAA , 1, 1) ///< Whether or not to use distinct TBAA tags for pointers.
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CODEGENOPT(StructPathTBAA , 1, 0) ///< Whether or not to use struct-path TBAA.
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CODEGENOPT(NewStructPathTBAA , 1, 0) ///< Whether or not to use enhanced struct-path TBAA.
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CODEGENOPT(SaveTempLabels , 1, 0) ///< Save temporary labels.

‎clang/include/clang/Driver/Options.td

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@@ -7361,9 +7361,12 @@ def fuse_register_sized_bitfield_access: Flag<["-"], "fuse-register-sized-bitfie
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def relaxed_aliasing : Flag<["-"], "relaxed-aliasing">,
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HelpText<"Turn off Type Based Alias Analysis">,
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MarshallingInfoFlag<CodeGenOpts<"RelaxedAliasing">>;
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def pointer_tbaa: Flag<["-"], "pointer-tbaa">,
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HelpText<"Turn on Type Based Alias Analysis for pointer accesses">,
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MarshallingInfoFlag<CodeGenOpts<"PointerTBAA">>;
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defm pointer_tbaa: BoolOption<"", "pointer-tbaa", CodeGenOpts<"PointerTBAA">,
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DefaultTrue,
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PosFlag<SetTrue, [], [ClangOption], "Enable">,
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NegFlag<SetFalse, [], [ClangOption], "Disable">,
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BothFlags<[], [ClangOption], " that single precision floating-point divide and sqrt used in ">>
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;
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def no_struct_path_tbaa : Flag<["-"], "no-struct-path-tbaa">,
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HelpText<"Turn off struct-path aware Type Based Alias Analysis">,
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MarshallingInfoNegativeFlag<CodeGenOpts<"StructPathTBAA">>;

‎clang/lib/Driver/ToolChains/Clang.cpp

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@@ -5935,9 +5935,9 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
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if (!Args.hasFlag(options::OPT_fstrict_aliasing, StrictAliasingAliasOption,
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options::OPT_fno_strict_aliasing, !IsWindowsMSVC))
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CmdArgs.push_back("-relaxed-aliasing");
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if (Args.hasFlag(options::OPT_fpointer_tbaa, options::OPT_fno_pointer_tbaa,
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if (Args.hasFlag(options::OPT_fno_pointer_tbaa, options::OPT_fpointer_tbaa,
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false))
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CmdArgs.push_back("-pointer-tbaa");
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CmdArgs.push_back("-no-pointer-tbaa");
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if (!Args.hasFlag(options::OPT_fstruct_path_tbaa,
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options::OPT_fno_struct_path_tbaa, true))
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CmdArgs.push_back("-no-struct-path-tbaa");

‎clang/test/CodeGen/attr-counted-by.c

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‎clang/test/CodeGen/tbaa-pointers.c

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‎clang/test/CodeGen/tbaa-reference.cpp

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@@ -1,7 +1,7 @@
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// RUN: %clang_cc1 -triple x86_64-linux -O1 -disable-llvm-passes %s -emit-llvm -o - | FileCheck %s -check-prefixes=CHECK,OLD-PATH
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// RUN: %clang_cc1 -triple x86_64-linux -O1 -disable-llvm-passes -pointer-tbaa %s -emit-llvm -o - | FileCheck %s -check-prefixes=CHECK,OLD-PATH-POINTER
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// RUN: %clang_cc1 -triple x86_64-linux -O1 -disable-llvm-passes %s -emit-llvm -new-struct-path-tbaa -o - | FileCheck %s -check-prefixes=CHECK,NEW-PATH
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// RUN: %clang_cc1 -triple x86_64-linux -O1 -disable-llvm-passes %s -pointer-tbaa -emit-llvm -new-struct-path-tbaa -o - | FileCheck %s -check-prefixes=CHECK,NEW-PATH-POINTER
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// RUN: %clang_cc1 -triple x86_64-linux -O1 -disable-llvm-passes -no-pointer-tbaa %s -emit-llvm -o - | FileCheck %s -check-prefixes=CHECK,OLD-PATH
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// RUN: %clang_cc1 -triple x86_64-linux -O1 -disable-llvm-passes %s -emit-llvm -o - | FileCheck %s -check-prefixes=CHECK,OLD-PATH-POINTER
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// RUN: %clang_cc1 -triple x86_64-linux -O1 -disable-llvm-passes %s -no-pointer-tbaa -emit-llvm -new-struct-path-tbaa -o - | FileCheck %s -check-prefixes=CHECK,NEW-PATH
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// RUN: %clang_cc1 -triple x86_64-linux -O1 -disable-llvm-passes %s -emit-llvm -new-struct-path-tbaa -o - | FileCheck %s -check-prefixes=CHECK,NEW-PATH-POINTER
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//
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// Check that we generate correct TBAA information for reference accesses.
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‎clang/test/CodeGenCXX/template-instantiation.cpp

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@@ -17,6 +17,7 @@
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// CHECK2-NOT: _ZTVN5test31SIiEE
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// CHECK2-NOT: _ZTSN5test31SIiEE
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// CHECK2: !{!"p1 _ZTSN5test31SIiEE",
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// CHECK-LABEL: define linkonce_odr void @_ZN5test21CIiEC1Ev(ptr {{[^,]*}} %this) unnamed_addr
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// CHECK-LABEL: define linkonce_odr void @_ZN5test21CIiE6foobarIdEEvT_(

‎clang/test/CodeGenOpenCL/amdgpu-enqueue-kernel.cl

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‎clang/test/OpenMP/nvptx_target_parallel_reduction_codegen_tbaa_PR46146.cpp

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‎clang/unittests/CodeGen/TBAAMetadataTest.cpp

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@@ -39,6 +39,11 @@ auto OmnipotentCharC = MMTuple(
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MConstInt(0, 64)
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);
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auto AnyPtr = MMTuple(
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MMString("any pointer"),
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OmnipotentCharC,
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MConstInt(0, 64)
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);
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auto OmnipotentCharCXX = MMTuple(
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MMString("omnipotent char"),
@@ -116,8 +121,8 @@ TEST(TBAAMetadataTest, BasicTypes) {
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MValType(PointerType::getUnqual(Compiler.Context)),
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MMTuple(
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MMTuple(
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MMString("any pointer"),
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OmnipotentCharC,
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MMString("p1 void"),
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AnyPtr,
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MConstInt(0)),
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MSameAs(0),
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MConstInt(0))));
@@ -128,8 +133,8 @@ TEST(TBAAMetadataTest, BasicTypes) {
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MValType(PointerType::getUnqual(Compiler.Context)),
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MMTuple(
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MMTuple(
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MMString("any pointer"),
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OmnipotentCharC,
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MMString("p1 int"),
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AnyPtr,
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MConstInt(0)),
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MSameAs(0),
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MConstInt(0))));

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