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[Driver] Clean up denormal handling with fast-math-related options #89477

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Merged
merged 8 commits into from
Apr 29, 2024
Merged

[Driver] Clean up denormal handling with fast-math-related options #89477

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8ab931c
Clean up denormal handling with -ffp-model, -ffast-math, etc.
Apr 20, 2024
bf1e013
Update FP option rendering to leave denormal-fp-math alone
Apr 24, 2024
f1f643c
User manual updates
Apr 24, 2024
0614850
Formatting fixes
Apr 25, 2024
4fc3057
Fix fp-model.c test and UsersManual.rst
Apr 25, 2024
a7e4f5c
Updates based on review feedback
Apr 26, 2024
fb98b1a
Minor documentation edit
Apr 26, 2024
42e59d2
Resolve merge conflict
Apr 29, 2024
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15 changes: 9 additions & 6 deletions clang/docs/UsersManual.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -1452,8 +1452,6 @@ floating point semantic models: precise (the default), strict, and fast.
"fenv_access", "off", "on", "off"
"rounding_mode", "tonearest", "dynamic", "tonearest"
"contract", "on", "off", "fast"
"denormal_fp_math", "IEEE", "IEEE", "IEEE"
"denormal_fp32_math", "IEEE","IEEE", "IEEE"
"support_math_errno", "on", "on", "off"
"no_honor_nans", "off", "off", "on"
"no_honor_infinities", "off", "off", "on"
Expand All @@ -1462,6 +1460,14 @@ floating point semantic models: precise (the default), strict, and fast.
"allow_approximate_fns", "off", "off", "on"
"allow_reassociation", "off", "off", "on"

The ``-ffp-model`` option does not modify the ``fdenormal-fp-math``
setting, but it does have an impact on whether ``crtfastmath.o`` is
linked. Because linking ``crtfastmath.o`` has a global effect on the
program, and because the global denormal handling can be changed in
other ways, the state of ``fdenormal-fp-math`` handling cannot
be assumed in any function based on fp-model. See :ref:`crtfastmath.o`
for more details.

.. option:: -ffast-math

Enable fast-math mode. This option lets the
Expand Down Expand Up @@ -1537,7 +1543,6 @@ floating point semantic models: precise (the default), strict, and fast.
Also, this option resets following options to their target-dependent defaults.

* ``-f[no-]math-errno``
* ``-fdenormal-fp-math=<value>``

There is ambiguity about how ``-ffp-contract``, ``-ffast-math``,
and ``-fno-fast-math`` behave when combined. To keep the value of
Expand All @@ -1560,8 +1565,7 @@ floating point semantic models: precise (the default), strict, and fast.
``-ffp-contract`` setting is determined by the default value of
``-ffp-contract``.

Note: ``-fno-fast-math`` implies ``-fdenormal-fp-math=ieee``.
``-fno-fast-math`` causes ``crtfastmath.o`` to not be linked with code
Note: ``-fno-fast-math`` causes ``crtfastmath.o`` to not be linked with code
unless ``-mdaz-ftz`` is present.

.. option:: -fdenormal-fp-math=<value>
Expand Down Expand Up @@ -1694,7 +1698,6 @@ floating point semantic models: precise (the default), strict, and fast.
* ``-fsigned-zeros``
* ``-ftrapping-math``
* ``-ffp-contract=on``
* ``-fdenormal-fp-math=ieee``

There is ambiguity about how ``-ffp-contract``,
``-funsafe-math-optimizations``, and ``-fno-unsafe-math-optimizations``
Expand Down
13 changes: 9 additions & 4 deletions clang/lib/Driver/ToolChain.cpp
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Expand Up @@ -1316,14 +1316,19 @@ bool ToolChain::isFastMathRuntimeAvailable(const ArgList &Args,
// (to keep the linker options consistent with gcc and clang itself).
if (Default && !isOptimizationLevelFast(Args)) {
// Check if -ffast-math or -funsafe-math.
Arg *A =
Args.getLastArg(options::OPT_ffast_math, options::OPT_fno_fast_math,
options::OPT_funsafe_math_optimizations,
options::OPT_fno_unsafe_math_optimizations);
Arg *A = Args.getLastArg(
options::OPT_ffast_math, options::OPT_fno_fast_math,
options::OPT_funsafe_math_optimizations,
options::OPT_fno_unsafe_math_optimizations, options::OPT_ffp_model_EQ);

if (!A || A->getOption().getID() == options::OPT_fno_fast_math ||
A->getOption().getID() == options::OPT_fno_unsafe_math_optimizations)
Default = false;
if (A && A->getOption().getID() == options::OPT_ffp_model_EQ) {
StringRef Model = A->getValue();
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Nit: A->getValue() != "fast"

inline used-once variable and prefer == != for StringRef, which are much more common than equals.

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I hope to add -ffp-model=aggressive soon, with will require a second use of Model here.

if (Model != "fast")
Default = false;
}
}

// Whatever decision came as a result of the above implicit settings, either
Expand Down
20 changes: 3 additions & 17 deletions clang/lib/Driver/ToolChains/Clang.cpp
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Expand Up @@ -2743,13 +2743,11 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
StringRef FPExceptionBehavior = "";
// -ffp-eval-method options: double, extended, source
StringRef FPEvalMethod = "";
const llvm::DenormalMode DefaultDenormalFPMath =
llvm::DenormalMode DenormalFPMath =
TC.getDefaultDenormalModeForType(Args, JA);
const llvm::DenormalMode DefaultDenormalFP32Math =
llvm::DenormalMode DenormalFP32Math =
TC.getDefaultDenormalModeForType(Args, JA, &llvm::APFloat::IEEEsingle());

llvm::DenormalMode DenormalFPMath = DefaultDenormalFPMath;
llvm::DenormalMode DenormalFP32Math = DefaultDenormalFP32Math;
// CUDA and HIP don't rely on the frontend to pass an ffp-contract option.
// If one wasn't given by the user, don't pass it here.
StringRef FPContract;
Expand Down Expand Up @@ -2899,11 +2897,6 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
SignedZeros = true;
// -fno_fast_math restores default denormal and fpcontract handling
FPContract = "on";
DenormalFPMath = llvm::DenormalMode::getIEEE();

// FIXME: The target may have picked a non-IEEE default mode here based on
// -cl-denorms-are-zero. Should the target consider -fp-model interaction?
DenormalFP32Math = llvm::DenormalMode::getIEEE();

StringRef Val = A->getValue();
if (OFastEnabled && !Val.equals("fast")) {
Expand Down Expand Up @@ -3122,9 +3115,6 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
TrappingMath = true;
FPExceptionBehavior = "strict";

// The target may have opted to flush by default, so force IEEE.
DenormalFPMath = llvm::DenormalMode::getIEEE();
DenormalFP32Math = llvm::DenormalMode::getIEEE();
if (!JA.isDeviceOffloading(Action::OFK_Cuda) &&
!JA.isOffloading(Action::OFK_HIP)) {
if (LastSeenFfpContractOption != "") {
Expand Down Expand Up @@ -3154,9 +3144,7 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
ReciprocalMath = false;
ApproxFunc = false;
SignedZeros = true;
// -fno_fast_math restores default denormal and fpcontract handling
DenormalFPMath = DefaultDenormalFPMath;
DenormalFP32Math = llvm::DenormalMode::getIEEE();
// -fno_fast_math restores default fpcontract handling
if (!JA.isDeviceOffloading(Action::OFK_Cuda) &&
!JA.isOffloading(Action::OFK_HIP)) {
if (LastSeenFfpContractOption != "") {
Expand All @@ -3171,8 +3159,6 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
// subsequent options conflict then emit warning diagnostic.
if (HonorINFs && HonorNaNs && !AssociativeMath && !ReciprocalMath &&
SignedZeros && TrappingMath && RoundingFPMath && !ApproxFunc &&
DenormalFPMath == llvm::DenormalMode::getIEEE() &&
DenormalFP32Math == llvm::DenormalMode::getIEEE() &&
FPContract.equals("off"))
// OK: Current Arg doesn't conflict with -ffp-model=strict
;
Expand Down
9 changes: 5 additions & 4 deletions clang/test/Driver/fp-model.c
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Expand Up @@ -64,7 +64,8 @@

// RUN: %clang -### -ffp-model=strict -fdenormal-fp-math=preserve-sign,preserve-sign -c %s 2>&1 \
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You can use -### -Werror to ensure that there is no warning.

(In the absence of a --target=, you probably want to check a few different targets that the warning is printed regardless of the default target triple.)

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I didn't intend to change the logic of this test. The behavior here should be target-independent now.

// RUN: | FileCheck --check-prefix=WARN10 %s
// WARN10: warning: overriding '-ffp-model=strict' option with '-fdenormal-fp-math=preserve-sign,preserve-sign' [-Woverriding-option]
// WARN10: "-cc1"
// WARN10-NOT: warning: overriding '-ffp-model=strict' option with '-fdenormal-fp-math=preserve-sign,preserve-sign' [-Woverriding-option]

// RUN: %clang -### -ffp-model=fast -ffp-model=strict -c %s 2>&1 | FileCheck \
// RUN: --check-prefix=WARN11 %s
Expand All @@ -73,9 +74,8 @@

// RUN: %clang -### -Ofast -ffp-model=strict -c %s 2>&1 | FileCheck \
// RUN: --check-prefix=WARN12 %s
// RUN: %clang -### -ffast-math -ffp-model=strict -c %s 2>&1 | FileCheck \
// RUN: --check-prefix=WARN12 %s
// WARN12-NOT: warning: overriding '-ffp-model=strict' option with '-ffp-model=strict' [-Woverriding-option]
// RUN: %clang -### -Werror -ffast-math -ffp-model=strict -c %s
// WARN12: warning: overriding '-ffp-model=strict' option with '-Ofast'

// RUN: %clang -### -ffp-model=strict -fapprox-func -c %s 2>&1 \
// RUN: | FileCheck --check-prefix=WARN13 %s
Expand Down Expand Up @@ -129,6 +129,7 @@
// RUN: | FileCheck --check-prefix=CHECK-NO-EXCEPT %s
// RUN: %clang -### -nostdinc -ffp-model=strict -Ofast -c %s 2>&1 \
// RUN: | FileCheck --check-prefix=CHECK-NO-EXCEPT %s
// CHECK-NO-EXCEPT: "-cc1"
// CHECK-NO-EXCEPT-NOT: "-ffp-exception-behavior=strict"

// RUN: %clang -### -nostdinc -ffp-exception-behavior=strict -c %s 2>&1 \
Expand Down
3 changes: 3 additions & 0 deletions clang/test/Driver/linux-ld.c
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Expand Up @@ -1417,6 +1417,9 @@
// RUN: %clang --target=x86_64-unknown-linux -no-pie -### %s -funsafe-math-optimizations\
// 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 -ffp-model=fast \
// 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 -Ofast\
// RUN: --sysroot=%S/Inputs/basic_linux_tree 2>&1 \
// RUN: | FileCheck --check-prefix=CHECK-CRTFASTMATH %s
Expand Down
3 changes: 3 additions & 0 deletions clang/test/Driver/solaris-ld.c
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Expand Up @@ -193,6 +193,9 @@
// RUN: %clang --target=sparc-sun-solaris2.11 -### %s -ffast-math \
// RUN: --sysroot=%S/Inputs/solaris_sparc_tree 2>&1 \
// RUN: | FileCheck --check-prefix=CHECK-CRTFASTMATH-SPARC32 %s
// RUN: %clang --target=sparc-sun-solaris2.11 -### %s -ffp-model=fast \
// RUN: --sysroot=%S/Inputs/solaris_sparc_tree 2>&1 \
// RUN: | FileCheck --check-prefix=CHECK-CRTFASTMATH-SPARC32 %s
// CHECK-CRTFASTMATH-SPARC32: "-isysroot" "[[SYSROOT:[^"]+]]"
// CHECK-CRTFASTMATH-SPARC32: "[[SYSROOT]]/usr/gcc/4.8/lib/gcc/sparc-sun-solaris2.11/4.8.2{{/|\\\\}}crtfastmath.o"
// CHECK-NOCRTFASTMATH-SPARC32-NOT: crtfastmath.o
Expand Down