llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT--> @llvm/pr-subscribers-clang Author: Andy Kaylor (andykaylor) <details> <summary>Changes</summary> This change modifies -ffp-model=fast to select options that more closely match -funsafe-math-optimizations, and introduces a new model, -ffp-model=aggressive which matches the existing behavior (except for a minor change in the fp-contract behavior). The primary motivation for this change is to make -ffp-model=fast more user friendly, particularly in light of LLVM's aggressive optimizations when -fno-honor-nans and -fno-honor-infinites are used. This was previously proposed here: https://discourse.llvm.org/t/making-ffp-model-fast-more-user-friendly/78402 --- Full diff: https://github.com/llvm/llvm-project/pull/100453.diff 6 Files Affected: - (modified) clang/docs/ReleaseNotes.rst (+11) - (modified) clang/docs/UsersManual.rst (+25-20) - (modified) clang/lib/Driver/ToolChain.cpp (+1-1) - (modified) clang/lib/Driver/ToolChains/Clang.cpp (+28-18) - (modified) clang/test/CodeGen/ffp-model.c (+27-8) - (modified) clang/test/Driver/fp-model.c (+2-2) ``````````diff diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst index 65de90f69e198..7e3fb64c0efb3 100644 --- a/clang/docs/ReleaseNotes.rst +++ b/clang/docs/ReleaseNotes.rst @@ -102,6 +102,17 @@ Deprecated Compiler Flags Modified Compiler Flags ----------------------- +- The ``-ffp-model`` option has been updated to enable a more limited set of + optimizations when the ``fast`` argument is used and to accept a new argument, + ``aggressive``. The behavior of ``-ffp-model=aggressive`` is mostly equivalent + to the previous behavior of ``-ffp-model=fast``. The updated + ``-ffp-model=fast`` behavior no longer assumes finite math only and uses a + the ``promoted`` algorithm for complex division when possible rather than the + less robust Smith algorithm. Both ``-ffp-model=fast`` and + ``-ffp-model=aggressive`` will now imply ``-ffp-contract=fast-honor-pragmas`` + rather than ``-ffp-contract=fast``. + + Removed Compiler Flags ------------------------- diff --git a/clang/docs/UsersManual.rst b/clang/docs/UsersManual.rst index e9b95739ea2ab..ea28e9e22bdfe 100644 --- a/clang/docs/UsersManual.rst +++ b/clang/docs/UsersManual.rst @@ -1452,28 +1452,30 @@ describes the various floating point semantic modes and the corresponding option "fhonor-infinities", "{on, off}" "fsigned-zeros", "{on, off}" "freciprocal-math", "{on, off}" - "allow_approximate_fns", "{on, off}" + "fallow-approximate-fns", "{on, off}" "fassociative-math", "{on, off}" + "fcomplex-arithmetic", "{basic, improved, full, promoted}" This table describes the option settings that correspond to the three floating point semantic models: precise (the default), strict, and fast. .. csv-table:: Floating Point Models - :header: "Mode", "Precise", "Strict", "Fast" - :widths: 25, 15, 15, 15 - - "except_behavior", "ignore", "strict", "ignore" - "fenv_access", "off", "on", "off" - "rounding_mode", "tonearest", "dynamic", "tonearest" - "contract", "on", "off", "fast" - "support_math_errno", "on", "on", "off" - "no_honor_nans", "off", "off", "on" - "no_honor_infinities", "off", "off", "on" - "no_signed_zeros", "off", "off", "on" - "allow_reciprocal", "off", "off", "on" - "allow_approximate_fns", "off", "off", "on" - "allow_reassociation", "off", "off", "on" + :header: "Mode", "Precise", "Strict", "Fast", "Aggressive" + :widths: 25, 25, 25, 25, 25 + + "except_behavior", "ignore", "strict", "ignore", "ignore" + "fenv_access", "off", "on", "off", "off" + "rounding_mode", "tonearest", "dynamic", "tonearest", "tonearest" + "contract", "on", "off", "fast-honor-pragmas", "fast-honor-pragmas" + "support_math_errno", "on", "on", "off", "off" + "no_honor_nans", "off", "off", "off", "on" + "no_honor_infinities", "off", "off", "off", "on" + "no_signed_zeros", "off", "off", "on", "on" + "allow_reciprocal", "off", "off", "on", "on" + "allow_approximate_fns", "off", "off", "on", "on" + "allow_reassociation", "off", "off", "on", "on" + "complex_arithmetic", "full", "full", "promoted", "basic" The ``-ffp-model`` option does not modify the ``fdenormal-fp-math`` setting, but it does have an impact on whether ``crtfastmath.o`` is @@ -1492,9 +1494,9 @@ for more details. * Floating-point math obeys regular algebraic rules for real numbers (e.g. ``+`` and ``*`` are associative, ``x/y == x * (1/y)``, and ``(a + b) * c == a * c + b * c``), - * Operands to floating-point operations are not equal to ``NaN`` and - ``Inf``, and - * ``+0`` and ``-0`` are interchangeable. + * No ``NaN`` or infinite values will be operands or results of + floating-point operations, + * ``+0`` and ``-0`` may be treated as interchangeable. ``-ffast-math`` also defines the ``__FAST_MATH__`` preprocessor macro. Some math libraries recognize this macro and change their behavior. @@ -1753,7 +1755,7 @@ for more details. Specify floating point behavior. ``-ffp-model`` is an umbrella option that encompasses functionality provided by other, single purpose, floating point options. Valid values are: ``precise``, ``strict``, - and ``fast``. + ``fast``, and ``aggressive``. Details: * ``precise`` Disables optimizations that are not value-safe on @@ -1766,7 +1768,10 @@ for more details. ``STDC FENV_ACCESS``: by default ``FENV_ACCESS`` is disabled. This option setting behaves as though ``#pragma STDC FENV_ACCESS ON`` appeared at the top of the source file. - * ``fast`` Behaves identically to specifying both ``-ffast-math`` and + * ``fast`` Behaves identically to specifying ``-funsafe-math-optimizations``, + ``-fno-math-errno`` and ``-fcomplex-arithmetic=promoted`` + ``ffp-contract=fast`` + * ``aggressive`` Behaves identically to specifying both ``-ffast-math`` and ``ffp-contract=fast`` Note: If your command line specifies multiple instances diff --git a/clang/lib/Driver/ToolChain.cpp b/clang/lib/Driver/ToolChain.cpp index 20a555afb8092..49555109b6173 100644 --- a/clang/lib/Driver/ToolChain.cpp +++ b/clang/lib/Driver/ToolChain.cpp @@ -1337,7 +1337,7 @@ bool ToolChain::isFastMathRuntimeAvailable(const ArgList &Args, Default = false; if (A && A->getOption().getID() == options::OPT_ffp_model_EQ) { StringRef Model = A->getValue(); - if (Model != "fast") + if (Model != "fast" && Model != "aggressive") Default = false; } } diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp index df1bb8e9ee308..41863eeea395c 100644 --- a/clang/lib/Driver/ToolChains/Clang.cpp +++ b/clang/lib/Driver/ToolChains/Clang.cpp @@ -2880,9 +2880,19 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D, std::string GccRangeComplexOption = ""; // Lambda to set fast-math options. This is also used by -ffp-model=fast - auto applyFastMath = [&]() { - HonorINFs = false; - HonorNaNs = false; + auto applyFastMath = [&](bool Aggressive) { + LangOptions::ComplexRangeKind NewRange; + if (Aggressive) { + HonorINFs = false; + HonorNaNs = false; + FPContract = "fast"; + NewRange = LangOptions::ComplexRangeKind::CX_Basic; + } else { + HonorINFs = true; + HonorNaNs = true; + FPContract = "fast-honor-pragmas"; + NewRange = LangOptions::ComplexRangeKind::CX_Promoted; + } MathErrno = false; AssociativeMath = true; ReciprocalMath = true; @@ -2891,21 +2901,16 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D, TrappingMath = false; RoundingFPMath = false; FPExceptionBehavior = ""; - // If fast-math is set then set the fp-contract mode to fast. - FPContract = "fast"; - // ffast-math enables basic range rules for complex multiplication and - // division. // Warn if user expects to perform full implementation of complex // multiplication or division in the presence of nan or ninf flags. - if (Range == LangOptions::ComplexRangeKind::CX_Full || - Range == LangOptions::ComplexRangeKind::CX_Improved || - Range == LangOptions::ComplexRangeKind::CX_Promoted) + if (Range != NewRange) EmitComplexRangeDiag( - D, ComplexArithmeticStr(Range), + D, !GccRangeComplexOption.empty() ? GccRangeComplexOption - : ComplexArithmeticStr(LangOptions::ComplexRangeKind::CX_Basic)); - Range = LangOptions::ComplexRangeKind::CX_Basic; + : ComplexArithmeticStr(Range), + ComplexArithmeticStr(NewRange)); + Range = NewRange; SeenUnsafeMathModeOption = true; }; @@ -3033,8 +3038,8 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D, SignedZeros = true; StringRef Val = A->getValue(); - if (OFastEnabled && Val != "fast") { - // Only -ffp-model=fast is compatible with OFast, ignore. + if (OFastEnabled && Val != "aggressive") { + // Only -ffp-model=aggressive is compatible with OFast, ignore. D.Diag(clang::diag::warn_drv_overriding_option) << Args.MakeArgString("-ffp-model=" + Val) << "-Ofast"; break; @@ -3046,10 +3051,15 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D, << Args.MakeArgString("-ffp-model=" + Val); if (Val == "fast") { FPModel = Val; - applyFastMath(); + applyFastMath(false); // applyFastMath sets fp-contract="fast" LastFpContractOverrideOption = "-ffp-model=fast"; - } else if (Val == "precise") { + } else if (Val.equals("aggressive")) { + FPModel = Val; + applyFastMath(true); + // applyFastMath sets fp-contract="fast" + LastFpContractOverrideOption = "-ffp-model=aggressive"; + } else if (Val.equals("precise")) { FPModel = Val; FPContract = "on"; LastFpContractOverrideOption = "-ffp-model=precise"; @@ -3241,7 +3251,7 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D, continue; [[fallthrough]]; case options::OPT_ffast_math: - applyFastMath(); + applyFastMath(true); if (A->getOption().getID() == options::OPT_Ofast) LastFpContractOverrideOption = "-Ofast"; else diff --git a/clang/test/CodeGen/ffp-model.c b/clang/test/CodeGen/ffp-model.c index 4ed9b9dc0a780..5516ccb218b03 100644 --- a/clang/test/CodeGen/ffp-model.c +++ b/clang/test/CodeGen/ffp-model.c @@ -3,6 +3,9 @@ // RUN: %clang -S -emit-llvm -fenable-matrix -ffp-model=fast %s -o - \ // RUN: | FileCheck %s --check-prefixes=CHECK,CHECK-FAST +// RUN: %clang -S -emit-llvm -fenable-matrix -ffp-model=aggressive %s -o - \ +// RUN: | FileCheck %s --check-prefixes=CHECK,CHECK-AGGRESSIVE + // RUN: %clang -S -emit-llvm -fenable-matrix -ffp-model=precise %s -o - \ // RUN: | FileCheck %s --check-prefixes=CHECK,CHECK-PRECISE @@ -20,9 +23,13 @@ float mymuladd(float x, float y, float z) { // CHECK: define{{.*}} float @mymuladd return x * y + z; - // CHECK-FAST: fmul fast float + // CHECK-AGGRESSIVE: fmul fast float + // CHECK-AGGRESSIVE: load float, ptr + // CHECK-AGGRESSIVE: fadd fast float + + // CHECK-FAST: fmul reassoc nsz arcp contract afn float // CHECK-FAST: load float, ptr - // CHECK-FAST: fadd fast float + // CHECK-FAST: fadd reassoc nsz arcp contract afn float // CHECK-PRECISE: load float, ptr // CHECK-PRECISE: load float, ptr @@ -54,9 +61,13 @@ void my_vec_muladd(v2f x, float y, v2f z, v2f *res) { // CHECK: define{{.*}}@my_vec_muladd *res = x * y + z; - // CHECK-FAST: fmul fast <2 x float> + // CHECK-AGGRESSIVE: fmul fast <2 x float> + // CHECK-AGGRESSIVE: load <2 x float>, ptr + // CHECK-AGGRESSIVE: fadd fast <2 x float> + + // CHECK-FAST: fmul reassoc nsz arcp contract afn <2 x float> // CHECK-FAST: load <2 x float>, ptr - // CHECK-FAST: fadd fast <2 x float> + // CHECK-FAST: fadd reassoc nsz arcp contract afn <2 x float> // CHECK-PRECISE: load <2 x float>, ptr // CHECK-PRECISE: load float, ptr @@ -88,9 +99,13 @@ void my_m21_muladd(m21f x, float y, m21f z, m21f *res) { // CHECK: define{{.*}}@my_m21_muladd *res = x * y + z; - // CHECK-FAST: fmul fast <2 x float> + // CHECK-AGGRESSIVE: fmul fast <2 x float> + // CHECK-AGGRESSIVE: load <2 x float>, ptr + // CHECK-AGGRESSIVE: fadd fast <2 x float> + + // CHECK-FAST: fmul reassoc nsz arcp contract afn <2 x float> // CHECK-FAST: load <2 x float>, ptr - // CHECK-FAST: fadd fast <2 x float> + // CHECK-FAST: fadd reassoc nsz arcp contract afn <2 x float> // CHECK-PRECISE: load <2 x float>, ptr // CHECK-PRECISE: load float, ptr @@ -122,9 +137,13 @@ void my_m22_muladd(m22f x, float y, m22f z, m22f *res) { // CHECK: define{{.*}}@my_m22_muladd *res = x * y + z; - // CHECK-FAST: fmul fast <4 x float> + // CHECK-AGGRESSIVE: fmul fast <4 x float> + // CHECK-AGGRESSIVE: load <4 x float>, ptr + // CHECK-AGGRESSIVE: fadd fast <4 x float> + + // CHECK-FAST: fmul reassoc nsz arcp contract afn <4 x float> // CHECK-FAST: load <4 x float>, ptr - // CHECK-FAST: fadd fast <4 x float> + // CHECK-FAST: fadd reassoc nsz arcp contract afn <4 x float> // CHECK-PRECISE: load <4 x float>, ptr // CHECK-PRECISE: load float, ptr diff --git a/clang/test/Driver/fp-model.c b/clang/test/Driver/fp-model.c index 2348d4b41f43a..d15dcad725a8f 100644 --- a/clang/test/Driver/fp-model.c +++ b/clang/test/Driver/fp-model.c @@ -2,11 +2,11 @@ // and other floating point options get a warning diagnostic. // -// RUN: %clang -### -ffp-model=fast -ffp-contract=off -c %s 2>&1 \ +// RUN: %clang -### -ffp-model=aggressive -ffp-contract=off -c %s 2>&1 \ // RUN: | FileCheck --check-prefix=WARN %s // WARN: warning: overriding '-ffp-model=fast' option with '-ffp-contract=off' [-Woverriding-option] -// RUN: %clang -### -ffp-model=fast -ffp-contract=on -c %s 2>&1 \ +// RUN: %clang -### -ffp-model=aggressive -ffp-contract=on -c %s 2>&1 \ // RUN: | FileCheck --check-prefix=WARN1 %s // WARN1: warning: overriding '-ffp-model=fast' option with '-ffp-contract=on' [-Woverriding-option] `````````` </details> https://github.com/llvm/llvm-project/pull/100453 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
