https://github.com/jcranmer-intel updated https://github.com/llvm/llvm-project/pull/80475
>From fc0507f013f556cc7c49a38f22d14578311f1f42 Mon Sep 17 00:00:00 2001 From: Joshua Cranmer <joshua.cran...@intel.com> Date: Fri, 2 Feb 2024 10:35:29 -0800 Subject: [PATCH 1/3] Disable FTZ/DAZ when compiling shared libraries by default. This fixes https://github.com/llvm/llvm-project/issues/57589, and aligns Clang with the behavior of current versions of gcc. There is a new option, -mdaz-ftz, to control the linking of the file that sets FTZ/DAZ on startup, and this flag is on by default if -ffast-math is present and -shared isn't. --- clang/docs/ReleaseNotes.rst | 5 ++++ clang/docs/UsersManual.rst | 15 ++++++++---- clang/include/clang/Driver/Options.td | 5 ++++ clang/lib/Driver/ToolChain.cpp | 15 ++++++++++-- clang/test/Driver/linux-ld.c | 34 +++++++++++++++++++++++++++ 5 files changed, 67 insertions(+), 7 deletions(-) diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst index 74bb9a07f0b13f..723a2bc859219b 100644 --- a/clang/docs/ReleaseNotes.rst +++ b/clang/docs/ReleaseNotes.rst @@ -145,6 +145,11 @@ Non-comprehensive list of changes in this release - ``__builtin_addc``, ``__builtin_subc``, and the other sizes of those builtins are now constexpr and may be used in constant expressions. +* Code compiled with ``-shared`` and ``-ffast-math`` will no longer enable + flush-to-zero floating-point mode by default. This decision can be overridden + with use of ``-mdaz-ftz``. This behavior now matches GCC's behavior. + (`#57589 <https://github.com/llvm/llvm-project/issues/57589>`_) + New Compiler Flags ------------------ diff --git a/clang/docs/UsersManual.rst b/clang/docs/UsersManual.rst index 7391e4cf3a9aeb..257af3c8d4d39a 100644 --- a/clang/docs/UsersManual.rst +++ b/clang/docs/UsersManual.rst @@ -1506,7 +1506,8 @@ floating point semantic models: precise (the default), strict, and fast. * ``-ffp-contract=fast`` - Note: ``-ffast-math`` causes ``crtfastmath.o`` to be linked with code. See + Note: ``-ffast-math`` causes ``crtfastmath.o`` to be linked with code unless + ``-shared`` or ``-mno-daz-ftz`` is present. See :ref:`crtfastmath.o` for more details. .. option:: -fno-fast-math @@ -1560,7 +1561,8 @@ floating point semantic models: precise (the default), strict, and fast. ``-ffp-contract``. Note: ``-fno-fast-math`` implies ``-fdenormal-fp-math=ieee``. - ``-fno-fast-math`` causes ``crtfastmath.o`` to not be linked with code. + ``-fno-fast-math`` causes ``crtfastmath.o`` to not be linked with code + unless ``-mdaz-ftz`` is present. .. option:: -fdenormal-fp-math=<value> @@ -1907,10 +1909,13 @@ by using ``#pragma STDC FENV_ROUND`` with a value other than ``FE_DYNAMIC``. A note about ``crtfastmath.o`` ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -``-ffast-math`` and ``-funsafe-math-optimizations`` cause ``crtfastmath.o`` to be -automatically linked, which adds a static constructor that sets the FTZ/DAZ +``-ffast-math`` and ``-funsafe-math-optimizations`` without the ``-shared`` +option cause ``crtfastmath.o`` to be +automatically linked, which adds a static constructor that sets the FTZ/DAZ bits in MXCSR, affecting not only the current compilation unit but all static -and shared libraries included in the program. +and shared libraries included in the program. This decision can be overridden +by using either the flag ``-mdaz-ftz`` or ``-mno-daz-ftz`` to respectively +link or not link ``crtfastmath.o``. .. _FLT_EVAL_METHOD: diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td index 3a028fadb25b18..c607e2e5c6ca5f 100644 --- a/clang/include/clang/Driver/Options.td +++ b/clang/include/clang/Driver/Options.td @@ -2581,6 +2581,11 @@ defm protect_parens : BoolFOption<"protect-parens", "floating-point expressions are evaluated">, NegFlag<SetFalse>>; +defm daz_ftz : SimpleMFlag<"daz-ftz", + "Globally set", "Do not globally set", + " the denormals-are-zero (DAZ) and flush-to-zero (FTZ) bits in the " + "floating-point control register on program startup.">; + def ffor_scope : Flag<["-"], "ffor-scope">, Group<f_Group>; def fno_for_scope : Flag<["-"], "fno-for-scope">, Group<f_Group>; diff --git a/clang/lib/Driver/ToolChain.cpp b/clang/lib/Driver/ToolChain.cpp index f8c13c86daf9b0..08301b89ebb33e 100644 --- a/clang/lib/Driver/ToolChain.cpp +++ b/clang/lib/Driver/ToolChain.cpp @@ -1292,9 +1292,14 @@ void ToolChain::AddCCKextLibArgs(const ArgList &Args, bool ToolChain::isFastMathRuntimeAvailable(const ArgList &Args, std::string &Path) const { + // Don't implicitly link in mode-changing libraries in a shared library, since + // this can have very deleterious effects. See the various links from + // https://github.com/llvm/llvm-project/issues/57589 for more information. + bool Default = !Args.hasArg(options::OPT_shared); + // Do not check for -fno-fast-math or -fno-unsafe-math when -Ofast passed // (to keep the linker options consistent with gcc and clang itself). - if (!isOptimizationLevelFast(Args)) { + if (Default && !isOptimizationLevelFast(Args)) { // Check if -ffast-math or -funsafe-math. Arg *A = Args.getLastArg(options::OPT_ffast_math, options::OPT_fno_fast_math, @@ -1303,8 +1308,14 @@ bool ToolChain::isFastMathRuntimeAvailable(const ArgList &Args, if (!A || A->getOption().getID() == options::OPT_fno_fast_math || A->getOption().getID() == options::OPT_fno_unsafe_math_optimizations) - return false; + Default = false; } + + // Whatever decision came as a result of the above implicit settings, either + // -mdaz-ftz or -mno-daz-ftz is capable of overriding it. + if (!Args.hasFlag(options::OPT_mdaz_ftz, options::OPT_mno_daz_ftz, Default)) + return false; + // If crtfastmath.o exists add it to the arguments. Path = GetFilePath("crtfastmath.o"); return (Path != "crtfastmath.o"); // Not found. diff --git a/clang/test/Driver/linux-ld.c b/clang/test/Driver/linux-ld.c index b3ce5ca307a6c3..e3d721e620e0d1 100644 --- a/clang/test/Driver/linux-ld.c +++ b/clang/test/Driver/linux-ld.c @@ -1569,6 +1569,40 @@ // RUN: --gcc-toolchain="" \ // RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \ // RUN: | FileCheck --check-prefix=CHECK-NOCRTFASTMATH %s +// Don't link crtfastmath.o with -shared +// RUN: %clang --target=x86_64-unknown-linux -no-pie -### %s -ffast-math -shared \ +// RUN: --gcc-toolchain="" \ +// RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \ +// RUN: | FileCheck --check-prefix=CHECK-NOCRTFASTMATH %s +// RUN: %clang --target=x86_64-unknown-linux -no-pie -### %s -Ofast -shared \ +// RUN: --gcc-toolchain="" \ +// RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \ +// RUN: | FileCheck --check-prefix=CHECK-NOCRTFASTMATH %s +// Check for effects of -mdaz-ftz +// RUN: %clang --target=x86_64-unknown-linux -no-pie -### %s -ffast-math -shared -mdaz-ftz \ +// RUN: --gcc-toolchain="" \ +// RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \ +// RUN: | FileCheck --check-prefix=CHECK-CRTFASTMATH %s +// RUN: %clang --target=x86_64-unknown-linux -no-pie -### %s -ffast-math -mdaz-ftz \ +// RUN: --gcc-toolchain="" \ +// RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \ +// RUN: | FileCheck --check-prefix=CHECK-CRTFASTMATH %s +// RUN: %clang --target=x86_64-unknown-linux -no-pie -### %s -mdaz-ftz \ +// RUN: --gcc-toolchain="" \ +// RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \ +// RUN: | FileCheck --check-prefix=CHECK-CRTFASTMATH %s +// RUN: %clang --target=x86_64-unknown-linux -no-pie -### %s -ffast-math -shared -mno-daz-ftz \ +// RUN: --gcc-toolchain="" \ +// RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \ +// RUN: | FileCheck --check-prefix=CHECK-NOCRTFASTMATH %s +// RUN: %clang --target=x86_64-unknown-linux -no-pie -### %s -ffast-math -mno-daz-ftz \ +// RUN: --gcc-toolchain="" \ +// RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \ +// RUN: | FileCheck --check-prefix=CHECK-NOCRTFASTMATH %s +// RUN: %clang --target=x86_64-unknown-linux -no-pie -### %s -mno-daz-ftz \ +// RUN: --gcc-toolchain="" \ +// RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \ +// RUN: | FileCheck --check-prefix=CHECK-NOCRTFASTMATH %s // CHECK-CRTFASTMATH: usr/lib/gcc/x86_64-unknown-linux/10.2.0{{/|\\\\}}crtfastmath.o // CHECK-NOCRTFASTMATH-NOT: crtfastmath.o >From 2ec10523c725c0ed7f88e8f02dac9be975beb19c Mon Sep 17 00:00:00 2001 From: Joshua Cranmer <joshua.cran...@intel.com> Date: Fri, 2 Feb 2024 11:01:04 -0800 Subject: [PATCH 2/3] Address review comments. --- clang/docs/ReleaseNotes.rst | 7 ++++--- clang/include/clang/Driver/Options.td | 2 +- clang/test/Driver/linux-ld.c | 12 ++---------- 3 files changed, 7 insertions(+), 14 deletions(-) diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst index 723a2bc859219b..67c163232ee6d7 100644 --- a/clang/docs/ReleaseNotes.rst +++ b/clang/docs/ReleaseNotes.rst @@ -145,9 +145,10 @@ Non-comprehensive list of changes in this release - ``__builtin_addc``, ``__builtin_subc``, and the other sizes of those builtins are now constexpr and may be used in constant expressions. -* Code compiled with ``-shared`` and ``-ffast-math`` will no longer enable - flush-to-zero floating-point mode by default. This decision can be overridden - with use of ``-mdaz-ftz``. This behavior now matches GCC's behavior. +* Shared libraries linked with either the ``-ffast-math``, ``-Ofast``, or + ``-funsafe-math-optimizations`` flags will no longer enable flush-to-zero + floating-point mode by default. This decision can be overridden with use of + ``-mdaz-ftz``. This behavior now matches GCC's behavior. (`#57589 <https://github.com/llvm/llvm-project/issues/57589>`_) New Compiler Flags diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td index c607e2e5c6ca5f..ac49a758bb685f 100644 --- a/clang/include/clang/Driver/Options.td +++ b/clang/include/clang/Driver/Options.td @@ -2584,7 +2584,7 @@ defm protect_parens : BoolFOption<"protect-parens", defm daz_ftz : SimpleMFlag<"daz-ftz", "Globally set", "Do not globally set", " the denormals-are-zero (DAZ) and flush-to-zero (FTZ) bits in the " - "floating-point control register on program startup.">; + "floating-point control register on program startup">; def ffor_scope : Flag<["-"], "ffor-scope">, Group<f_Group>; def fno_for_scope : Flag<["-"], "fno-for-scope">, Group<f_Group>; diff --git a/clang/test/Driver/linux-ld.c b/clang/test/Driver/linux-ld.c index e3d721e620e0d1..85b90d738ce340 100644 --- a/clang/test/Driver/linux-ld.c +++ b/clang/test/Driver/linux-ld.c @@ -1571,36 +1571,28 @@ // RUN: | FileCheck --check-prefix=CHECK-NOCRTFASTMATH %s // Don't link crtfastmath.o with -shared // RUN: %clang --target=x86_64-unknown-linux -no-pie -### %s -ffast-math -shared \ -// RUN: --gcc-toolchain="" \ // RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \ // RUN: | FileCheck --check-prefix=CHECK-NOCRTFASTMATH %s // RUN: %clang --target=x86_64-unknown-linux -no-pie -### %s -Ofast -shared \ -// RUN: --gcc-toolchain="" \ // RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \ // RUN: | FileCheck --check-prefix=CHECK-NOCRTFASTMATH %s // Check for effects of -mdaz-ftz -// RUN: %clang --target=x86_64-unknown-linux -no-pie -### %s -ffast-math -shared -mdaz-ftz \ -// RUN: --gcc-toolchain="" \ +// RUN: %clang --target=x86_64-unknown-linux -### %s -ffast-math -shared -mdaz-ftz \ // RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \ // RUN: | FileCheck --check-prefix=CHECK-CRTFASTMATH %s // RUN: %clang --target=x86_64-unknown-linux -no-pie -### %s -ffast-math -mdaz-ftz \ -// RUN: --gcc-toolchain="" \ // RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \ // RUN: | FileCheck --check-prefix=CHECK-CRTFASTMATH %s // RUN: %clang --target=x86_64-unknown-linux -no-pie -### %s -mdaz-ftz \ -// RUN: --gcc-toolchain="" \ // RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \ // RUN: | FileCheck --check-prefix=CHECK-CRTFASTMATH %s -// RUN: %clang --target=x86_64-unknown-linux -no-pie -### %s -ffast-math -shared -mno-daz-ftz \ -// RUN: --gcc-toolchain="" \ +// RUN: %clang --target=x86_64-unknown-linux -### %s -ffast-math -shared -mno-daz-ftz \ // RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \ // RUN: | FileCheck --check-prefix=CHECK-NOCRTFASTMATH %s // RUN: %clang --target=x86_64-unknown-linux -no-pie -### %s -ffast-math -mno-daz-ftz \ -// RUN: --gcc-toolchain="" \ // RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \ // RUN: | FileCheck --check-prefix=CHECK-NOCRTFASTMATH %s // RUN: %clang --target=x86_64-unknown-linux -no-pie -### %s -mno-daz-ftz \ -// RUN: --gcc-toolchain="" \ // RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \ // RUN: | FileCheck --check-prefix=CHECK-NOCRTFASTMATH %s // CHECK-CRTFASTMATH: usr/lib/gcc/x86_64-unknown-linux/10.2.0{{/|\\\\}}crtfastmath.o >From 4202a865f787fadd66cce847a4d317ebb037676c Mon Sep 17 00:00:00 2001 From: Joshua Cranmer <joshua.cran...@intel.com> Date: Thu, 22 Feb 2024 10:28:15 -0800 Subject: [PATCH 3/3] Partially revert fa7cd549d60. The guessing of whether or not FTZ/DAZ mode would be enabled is insufficiently accurate. --- clang/lib/Driver/ToolChains/Linux.cpp | 19 ------------------- clang/lib/Driver/ToolChains/Linux.h | 4 ---- clang/test/Driver/default-denormal-fp-math.c | 9 --------- 3 files changed, 32 deletions(-) diff --git a/clang/lib/Driver/ToolChains/Linux.cpp b/clang/lib/Driver/ToolChains/Linux.cpp index 4300a2bdff1791..31e4ef74442c02 100644 --- a/clang/lib/Driver/ToolChains/Linux.cpp +++ b/clang/lib/Driver/ToolChains/Linux.cpp @@ -834,25 +834,6 @@ void Linux::addProfileRTLibs(const llvm::opt::ArgList &Args, ToolChain::addProfileRTLibs(Args, CmdArgs); } -llvm::DenormalMode -Linux::getDefaultDenormalModeForType(const llvm::opt::ArgList &DriverArgs, - const JobAction &JA, - const llvm::fltSemantics *FPType) const { - switch (getTriple().getArch()) { - case llvm::Triple::x86: - case llvm::Triple::x86_64: { - std::string Unused; - // DAZ and FTZ are turned on in crtfastmath.o - if (!DriverArgs.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles) && - isFastMathRuntimeAvailable(DriverArgs, Unused)) - return llvm::DenormalMode::getPreserveSign(); - return llvm::DenormalMode::getIEEE(); - } - default: - return llvm::DenormalMode::getIEEE(); - } -} - void Linux::addExtraOpts(llvm::opt::ArgStringList &CmdArgs) const { for (const auto &Opt : ExtraOpts) CmdArgs.push_back(Opt.c_str()); diff --git a/clang/lib/Driver/ToolChains/Linux.h b/clang/lib/Driver/ToolChains/Linux.h index 524391743090ba..2d9e674e50a630 100644 --- a/clang/lib/Driver/ToolChains/Linux.h +++ b/clang/lib/Driver/ToolChains/Linux.h @@ -59,10 +59,6 @@ class LLVM_LIBRARY_VISIBILITY Linux : public Generic_ELF { std::vector<std::string> ExtraOpts; - llvm::DenormalMode getDefaultDenormalModeForType( - const llvm::opt::ArgList &DriverArgs, const JobAction &JA, - const llvm::fltSemantics *FPType = nullptr) const override; - const char *getDefaultLinker() const override; protected: diff --git a/clang/test/Driver/default-denormal-fp-math.c b/clang/test/Driver/default-denormal-fp-math.c index 5f87e151df49e4..c04ad5c08b8d0d 100644 --- a/clang/test/Driver/default-denormal-fp-math.c +++ b/clang/test/Driver/default-denormal-fp-math.c @@ -3,15 +3,6 @@ // RUN: %clang -### -target x86_64-unknown-linux-gnu --sysroot=%S/Inputs/basic_linux_tree -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s -// crtfastmath enables ftz and daz -// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffast-math --sysroot=%S/Inputs/basic_linux_tree -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-PRESERVESIGN %s - -// crt not linked in with nostartfiles -// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffast-math -nostartfiles --sysroot=%S/Inputs/basic_linux_tree -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s - -// If there's no crtfastmath, don't assume ftz/daz -// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffast-math --sysroot=/dev/null -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s - // RUN: %clang -### -target x86_64-scei-ps4 -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-PRESERVESIGN %s // Flag omitted for default _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
