forked from OSchip/llvm-project
Currently the options ‘ffast-math’ and ‘ffp-contract’ are connected.
When ‘ffast-math’ is set, ffp-contract is altered this way: -ffast-math/ Ofast -> ffp-contract=fast -fno-fast-math -> if ffp-contract= fast then ffp-contract=on else ffp-contract unchanged This differs from gcc which doesn’t connect the two options. Connecting these two options in clang, resulted in spurious warnings when the user combines these two options -ffast-math -fno-fast-math; see issue https://github.com/llvm/llvm-project/issues/54625. The issue is that the ‘ffast-math’ option is an on/off flag, but the ‘ffp-contract’ is an on/off/fast flag. So when ‘fno-fast-math’ is used there is no obvious value for ‘ffp-contract’. What should the value of ffp-contract be for -ffp-contract=fast -fno-fast-math and -ffast-math -ffp-contract=fast -fno-fast-math? The current logic sets ffp-contract back to on in these cases. This doesn’t take into account that the value of ffp-contract is modified by an explicit ffp-contract` option. This patch is proposing a set of rules to apply when ffp-contract', ffast-math and fno-fast-math are combined. These rules would give the user the expected behavior and no diagnostic would be needed. See RFC https://discourse.llvm.org/t/rfc-making-ffast-math-option-unrelated-to-ffp-contract-option/61912
This commit is contained in:
Zahira Ammarguellat
parent
00ce271712
commit
1b69ce1208
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@ -1359,8 +1359,8 @@ floating point semantic models: precise (the default), strict, and fast.
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"fenv_access", "off", "on", "off"
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"rounding_mode", "tonearest", "dynamic", "tonearest"
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"contract", "on", "off", "fast"
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"denormal_fp_math", "IEEE", "IEEE", "PreserveSign"
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"denormal_fp32_math", "IEEE","IEEE", "PreserveSign"
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"denormal_fp_math", "IEEE", "IEEE", "IEEE"
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"denormal_fp32_math", "IEEE","IEEE", "IEEE"
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"support_math_errno", "on", "on", "off"
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"no_honor_nans", "off", "off", "on"
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"no_honor_infinities", "off", "off", "on"
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@ -1408,6 +1408,61 @@ floating point semantic models: precise (the default), strict, and fast.
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* ``-ffp-contract=fast``
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Note: ``-ffast-math`` causes ``crtfastmath.o`` to be linked with code. See
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:ref:`crtfastmath.o` for more details.
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.. option:: -fno-fast-math
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Disable fast-math mode. This options disables unsafe floating-point
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optimizations by preventing the compiler from making any tranformations that
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could affect the results.
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This option implies:
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* ``-fhonor-infinities``
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* ``-fhonor-nans``
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* ``-fmath-errno``
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* ``-fno-finite-math-only``
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* ``-fno-associative-math``
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* ``-fno-reciprocal-math``
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* ``-fsigned-zeros``
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* ``-fno-trapping-math``
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* ``-ffp-contract=on``
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* ``-fdenormal-fp-math=ieee``
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There is ambiguity about how ``-ffp-contract``, ``-ffast-math``,
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and ``-fno-fast-math`` behave in combination. To keep the value of
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``-ffp-contract`` consistent, we define this set of rules:
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* ``-ffast-math`` sets ``ffp-contract`` to ``fast``.
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* ``-fno-fast-math`` sets ``-ffp-contract`` to ``on`` (``fast`` for CUDA and
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HIP).
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* If ``-ffast-math`` and ``-ffp-contract`` are both seen, but
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``-ffast-math`` is not followed by ``-fno-fast-math``, ``ffp-contract``
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will be given the value of whichever option was last seen.
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* If ``-fno-fast-math`` is seen and ``-ffp-contract`` has been seen at least
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once, the ``ffp-contract`` will get the value of the last seen value of
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``-ffp-contract``.
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* If ``-fno-fast-math`` is seen and ``-ffp-contract`` has not been seen, the
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``-ffp-contract`` setting is determined by the default value of
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``-ffp-contract``.
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Note: ``-fno-fast-math`` implies ``-fdenormal-fp-math=ieee``.
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``-fno-fast-math`` causes ``crtfastmath.o`` to not be linked with code.
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.. option:: -fdenormal-fp-math=<value>
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Select which denormal numbers the code is permitted to require.
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@ -1632,6 +1687,15 @@ Note that floating-point operations performed as part of constant initialization
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has no effect because the optimizer is prohibited from making unsafe
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transformations.
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.. _crtfastmath.o:
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A note about ``crtfastmath.o``
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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``-ffast-math`` and ``-funsafe-math-optimizations`` cause ``crtfastmath.o`` to be
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automatically linked, which adds a static constructor that sets the FTZ/DAZ
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bits in MXCSR, affecting not only the current compilation unit but all static
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and shared libraries included in the program.
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.. _FLT_EVAL_METHOD:
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A note about ``__FLT_EVAL_METHOD__``
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@ -2786,6 +2786,8 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
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// CUDA and HIP don't rely on the frontend to pass an ffp-contract option.
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// If one wasn't given by the user, don't pass it here.
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StringRef FPContract;
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StringRef LastSeenFfpContractOption;
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bool SeenFfastMathOption = false;
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if (!JA.isDeviceOffloading(Action::OFK_Cuda) &&
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!JA.isOffloading(Action::OFK_HIP))
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FPContract = "on";
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@ -2936,9 +2938,10 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
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// -ffp-model=precise sets PreciseFPModel to on and Val to
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// "precise". FPContract is set.
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;
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} else if (Val.equals("fast") || Val.equals("on") || Val.equals("off"))
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} else if (Val.equals("fast") || Val.equals("on") || Val.equals("off")) {
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FPContract = Val;
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else
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LastSeenFfpContractOption = Val;
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} else
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D.Diag(diag::err_drv_unsupported_option_argument)
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<< A->getOption().getName() << Val;
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break;
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@ -3031,6 +3034,7 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
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RoundingFPMath = false;
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// If fast-math is set then set the fp-contract mode to fast.
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FPContract = "fast";
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SeenFfastMathOption = true;
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break;
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case options::OPT_fno_fast_math:
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HonorINFs = true;
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@ -3047,12 +3051,11 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
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DenormalFPMath = DefaultDenormalFPMath;
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DenormalFP32Math = llvm::DenormalMode::getIEEE();
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if (!JA.isDeviceOffloading(Action::OFK_Cuda) &&
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!JA.isOffloading(Action::OFK_HIP))
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if (FPContract == "fast") {
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!JA.isOffloading(Action::OFK_HIP)) {
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if (LastSeenFfpContractOption != "") {
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FPContract = LastSeenFfpContractOption;
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} else if (SeenFfastMathOption)
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FPContract = "on";
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D.Diag(clang::diag::warn_drv_overriding_flag_option)
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<< "-ffp-contract=fast"
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<< "-ffp-contract=on";
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}
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break;
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}
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@ -35,7 +35,7 @@
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// RUN: | FileCheck %s --check-prefixes=CHECK,CHECK-FPC-ON
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// RUN: %clang -Xclang -no-opaque-pointers -S -emit-llvm -ffp-contract=fast -fno-fast-math \
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// RUN: %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-FPC-ON
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// RUN: %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-CONTRACTFAST
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// RUN: %clang -Xclang -no-opaque-pointers -S -emit-llvm -ffp-contract=on -fno-fast-math \
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// RUN: %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-FPC-ON
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@ -0,0 +1,114 @@
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// Test that -ffp-contract is set to the right value when combined with
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// the options -ffast-math and -fno-fast-math.
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// RUN: %clang -### -ffast-math -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-FAST %s
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// CHECK-FPC-FAST: "-ffp-contract=fast"
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// RUN: %clang -### -fno-fast-math -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-ON %s
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// RUN: %clang -### -ffast-math -ffp-contract=on -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-ON %s
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// CHECK-FPC-ON: "-ffp-contract=on"
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// RUN: %clang -### -ffast-math -ffp-contract=off -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-OFF %s
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// CHECK-FPC-OFF: "-ffp-contract=off"
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// RUN: %clang -### -ffast-math -ffp-contract=fast -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-FAST %s
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// RUN: %clang -### -ffp-contract=fast -ffast-math -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-FAST %s
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// RUN: %clang -### -ffp-contract=on -ffast-math -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-FAST %s
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// RUN: %clang -### -ffp-contract=off -ffast-math -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-FAST %s
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// RUN: %clang -### -ffp-contract=fast -fno-fast-math -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-FAST %s
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// RUN: %clang -### -ffp-contract=on -fno-fast-math -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-ON %s
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// RUN: %clang -### -ffp-contract=off -fno-fast-math -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-OFF %s
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// RUN: %clang -### -ffast-math -ffp-contract=fast -ffp-contract=on -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-ON %s
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// RUN: %clang -### -ffast-math -ffp-contract=on -ffp-contract=off -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-OFF %s
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// RUN: %clang -### -ffast-math -ffp-contract=on -ffp-contract=fast -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-FAST %s
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// RUN: %clang -### -ffast-math -ffp-contract=off -ffp-contract=on -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-ON %s
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// RUN: %clang -### -ffast-math -ffp-contract=off -ffp-contract=fast \
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// RUN: -c %s 2>&1 | FileCheck --check-prefix=CHECK-FPC-FAST %s
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// RUN: %clang -### -ffast-math -ffp-contract=on -fno-fast-math -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-ON %s
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// RUN: %clang -### -ffast-math -ffp-contract=off -fno-fast-math -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-OFF %s
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// RUN: %clang -### -ffast-math -ffp-contract=fast -fno-fast-math -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-FAST %s
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// RUN: %clang -### -ffast-math -fno-fast-math -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-ON %s
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// RUN: %clang -### -fno-fast-math -ffast-math -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-FAST %s
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// RUN: %clang -### -fno-fast-math -ffp-contract=on -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-ON %s
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// RUN: %clang -### -fno-fast-math -ffp-contract=off -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-OFF %s
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// RUN: %clang -### -fno-fast-math -ffp-contract=fast -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-FAST %s
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// RUN: %clang -### -ffp-contract=fast -fno-fast-math -ffp-contract=on \
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// RUN: -c %s 2>&1 | FileCheck --check-prefix=CHECK-FPC-ON %s
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// RUN: %clang -### -ffp-contract=fast -fno-fast-math -ffp-contract=off \
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// RUN: -c %s 2>&1 | FileCheck --check-prefix=CHECK-FPC-OFF %s
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// RUN: %clang -### -ffp-contract=off -fno-fast-math -ffp-contract=fast \
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// RUN: -c %s 2>&1 | FileCheck --check-prefix=CHECK-FPC-FAST %s
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// RUN: %clang -### -ffp-contract=off -fno-fast-math -ffp-contract=on \
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// RUN: -c %s 2>&1 | FileCheck --check-prefix=CHECK-FPC-ON %s
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// RUN: %clang -### -ffp-contract=on -ffast-math -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-FAST %s
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// RUN: %clang -### -ffp-contract=off -ffast-math -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-FAST %s
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// RUN: %clang -### -ffp-contract=fast -ffast-math -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-FAST %s
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// RUN: %clang -### -ffp-contract=on -ffast-math -fno-fast-math -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-ON %s
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// RUN: %clang -### -ffp-contract=off -ffast-math -fno-fast-math -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-OFF %s
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// RUN: %clang -### -ffp-contract=fast -ffast-math -fno-fast-math -c %s 2>&1 \
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// RUN: | FileCheck --check-prefix=CHECK-FPC-FAST %s
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// RUN: %clang -### -fno-fast-math -ffast-math -ffp-contract=fast \
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// RUN: -c %s 2>&1 | FileCheck --check-prefix=CHECK-FPC-FAST %s
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// RUN: %clang -### -fno-fast-math -ffast-math -ffp-contract=on \
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// RUN: -c %s 2>&1 | FileCheck --check-prefix=CHECK-FPC-ON %s
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// RUN: %clang -### -fno-fast-math -ffast-math -ffp-contract=off \
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// RUN: -c %s 2>&1 | FileCheck --check-prefix=CHECK-FPC-OFF %s
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