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[Driver] Clean up fp-contract handling in clang driver #91271

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[Driver] Clean up fp-contract handling in clang driver #91271

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90 changes: 53 additions & 37 deletions clang/lib/Driver/ToolChains/Clang.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2751,6 +2751,7 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
// If one wasn't given by the user, don't pass it here.
StringRef FPContract;
StringRef LastSeenFfpContractOption;
StringRef LastFpContractOverrideOption;
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Overridden seems more appropriate, but the variable name will become too long.
I wonder whether Last can be removed. It's clear from the type that this can only hold one option name.

bool SeenUnsafeMathModeOption = false;
if (!JA.isDeviceOffloading(Action::OFK_Cuda) &&
!JA.isOffloading(Action::OFK_HIP))
Expand Down Expand Up @@ -2792,6 +2793,27 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
SeenUnsafeMathModeOption = true;
};

// Lambda to consolidate common handling for fp-contract
auto restoreFPContractState = [&]() {
// CUDA and HIP don't rely on the frontend to pass an ffp-contract option.
// For other targets, if the state has been changed by one of the
// unsafe-math umbrella options a subsequent -fno-fast-math or
// -fno-unsafe-math-optimizations option reverts to the last value seen for
// the -ffp-contract option or "on" if we have not seen the -ffp-contract
// option. If we have not seen an unsafe-math option or -ffp-contract,
// we leave the FPContract state unchanged.
if (!JA.isDeviceOffloading(Action::OFK_Cuda) &&
!JA.isOffloading(Action::OFK_HIP)) {
if (LastSeenFfpContractOption != "")
FPContract = LastSeenFfpContractOption;
else if (SeenUnsafeMathModeOption)
FPContract = "on";
}
// In this case, we're reverting to the last explicit fp-contract option
// or the platform default
LastFpContractOverrideOption = "";
};

if (const Arg *A = Args.getLastArg(options::OPT_flimited_precision_EQ)) {
CmdArgs.push_back("-mlimit-float-precision");
CmdArgs.push_back(A->getValue());
Expand Down Expand Up @@ -2893,7 +2915,6 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
AssociativeMath = false;
ReciprocalMath = false;
SignedZeros = true;
FPContract = "on";
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Not quite sure why this is removed from here?

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It was unnecessary. Only one of the three fp-models sets FPContract to "on" and that's happening explicitly below. The code here is setting everything to what it would be for fp-model=precise and then resetting it immediately if we're handling -ffp-model=fast. Except for the FPContract state, these are right for fp-model strict as well.


StringRef Val = A->getValue();
if (OFastEnabled && !Val.equals("fast")) {
Expand All @@ -2910,14 +2931,18 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
if (Val.equals("fast")) {
FPModel = Val;
applyFastMath();
// applyFastMath sets fp-contract="fast"
LastFpContractOverrideOption = "-ffp-model=fast";
} else if (Val.equals("precise")) {
FPModel = Val;
FPContract = "on";
LastFpContractOverrideOption = "-ffp-model=precise";
} else if (Val.equals("strict")) {
StrictFPModel = true;
FPExceptionBehavior = "strict";
FPModel = Val;
FPContract = "off";
LastFpContractOverrideOption = "-ffp-model=strict";
TrappingMath = true;
RoundingFPMath = true;
} else
Expand Down Expand Up @@ -2996,8 +3021,15 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
StringRef Val = A->getValue();
if (Val.equals("fast") || Val.equals("on") || Val.equals("off") ||
Val.equals("fast-honor-pragmas")) {
if (Val != FPContract && LastFpContractOverrideOption != "") {
D.Diag(clang::diag::warn_drv_overriding_option)
<< LastFpContractOverrideOption
<< Args.MakeArgString("-ffp-contract=" + Val);
}

FPContract = Val;
LastSeenFfpContractOption = Val;
LastFpContractOverrideOption = "";
} else
D.Diag(diag::err_drv_unsupported_option_argument)
<< A->getSpelling() << Val;
Expand Down Expand Up @@ -3077,32 +3109,29 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
TrappingMath = false;
FPExceptionBehavior = "";
FPContract = "fast";
LastFpContractOverrideOption = "-funsafe-math-optimizations";
SeenUnsafeMathModeOption = true;
break;
case options::OPT_fno_unsafe_math_optimizations:
AssociativeMath = false;
ReciprocalMath = false;
SignedZeros = true;
ApproxFunc = false;

if (!JA.isDeviceOffloading(Action::OFK_Cuda) &&
!JA.isOffloading(Action::OFK_HIP)) {
if (LastSeenFfpContractOption != "") {
FPContract = LastSeenFfpContractOption;
} else if (SeenUnsafeMathModeOption)
FPContract = "on";
}
restoreFPContractState();
break;

case options::OPT_Ofast:
// If -Ofast is the optimization level, then -ffast-math should be enabled
if (!OFastEnabled)
continue;
[[fallthrough]];
case options::OPT_ffast_math: {
case options::OPT_ffast_math:
applyFastMath();
if (A->getOption().getID() == options::OPT_Ofast)
LastFpContractOverrideOption = "-Ofast";
else
LastFpContractOverrideOption = "-ffast-math";
break;
}
case options::OPT_fno_fast_math:
HonorINFs = true;
HonorNaNs = true;
Expand All @@ -3114,16 +3143,11 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
ReciprocalMath = false;
ApproxFunc = false;
SignedZeros = true;
// -fno_fast_math restores default fpcontract handling
if (!JA.isDeviceOffloading(Action::OFK_Cuda) &&
!JA.isOffloading(Action::OFK_HIP)) {
if (LastSeenFfpContractOption != "") {
FPContract = LastSeenFfpContractOption;
} else if (SeenUnsafeMathModeOption)
FPContract = "on";
}
restoreFPContractState();
LastFpContractOverrideOption = "";
break;
}
} // End switch (A->getOption().getID())

// The StrictFPModel local variable is needed to report warnings
// in the way we intend. If -ffp-model=strict has been used, we
// want to report a warning for the next option encountered that
Expand All @@ -3141,12 +3165,17 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
else {
StrictFPModel = false;
FPModel = "";
// The warning for -ffp-contract would have been reported by the
// OPT_ffp_contract_EQ handler above. A special check here is needed
// to avoid duplicating the warning.
auto RHS = (A->getNumValues() == 0)
? A->getSpelling()
: Args.MakeArgString(A->getSpelling() + A->getValue());
if (RHS != "-ffp-model=strict")
D.Diag(clang::diag::warn_drv_overriding_option)
<< "-ffp-model=strict" << RHS;
if (A->getSpelling() != "-ffp-contract=") {
if (RHS != "-ffp-model=strict")
D.Diag(clang::diag::warn_drv_overriding_option)
<< "-ffp-model=strict" << RHS;
}
}
}

Expand Down Expand Up @@ -3228,21 +3257,8 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
// individual features enabled by -ffast-math instead of the option itself as
// that's consistent with gcc's behaviour.
if (!HonorINFs && !HonorNaNs && !MathErrno && AssociativeMath && ApproxFunc &&
ReciprocalMath && !SignedZeros && !TrappingMath && !RoundingFPMath) {
ReciprocalMath && !SignedZeros && !TrappingMath && !RoundingFPMath)
CmdArgs.push_back("-ffast-math");
if (FPModel.equals("fast")) {
if (FPContract.equals("fast"))
// All set, do nothing.
;
else if (FPContract.empty())
// Enable -ffp-contract=fast
CmdArgs.push_back(Args.MakeArgString("-ffp-contract=fast"));
else
D.Diag(clang::diag::warn_drv_overriding_option)
<< "-ffp-model=fast"
<< Args.MakeArgString("-ffp-contract=" + FPContract);
}
}

// Handle __FINITE_MATH_ONLY__ similarly.
if (!HonorINFs && !HonorNaNs)
Expand Down
14 changes: 14 additions & 0 deletions clang/test/Driver/fp-contract.c
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Original file line number Diff line number Diff line change
Expand Up @@ -238,3 +238,17 @@
// RUN: %clang -### -fno-unsafe-math-optimizations -funsafe-math-optimizations \
// RUN: -ffp-contract=off -c %s 2>&1 | FileCheck --check-prefix=CHECK-FPC-OFF %s

// RUN: %clang -### -funsafe-math-optimizations -ffp-contract=off -c %s 2>&1 \
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L161 has similar -funsafe-math-optimizations -ffp-contract=off checks. The test can be folded there.

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I just went ahead and added a bunch of -Werror to previous lines in 514d80b

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That introduces a merge conflict for this patch. Is there a way I can solve that without having to do a rebase and force push for this, which kills the ability to see what changed between updates? I guess with a small-ish patch like this that's not a big problem, but it's something I try to avoid in general.

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Some folks prefer git merge origin/main while some just use git rebase origin/main and force push.

I am fine with either style, but someone really dislike force push (perhaps not for such a trivial change).

// RUN: | FileCheck --check-prefix=WARN %s
// WARN: warning: overriding '-funsafe-math-optimizations' option with '-ffp-contract=off'

// This case should not warn
// RUN: %clang -### -Werror -funsafe-math-optimizations \
// RUN: -fno-unsafe-math-optimizations -ffp-contract=off -c %s

// RUN: %clang -### -ffast-math -ffp-contract=off -c %s 2>&1 \
// RUN: | FileCheck --check-prefix=WARN2 %s
// WARN2: warning: overriding '-ffast-math' option with '-ffp-contract=off'

// This case should not warn
// RUN: %clang -### -Werror -ffast-math -fno-fast-math -ffp-contract=off -c %s
14 changes: 14 additions & 0 deletions clang/test/Driver/fp-model.c
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Expand Up @@ -81,6 +81,20 @@
// RUN: | FileCheck --check-prefix=WARN13 %s
// WARN13: warning: overriding '-ffp-model=strict' option with '-fapprox-func' [-Woverriding-option]

// RUN: %clang -### -ffp-model=precise -ffp-contract=off -c %s 2>&1 \
// RUN: | FileCheck --check-prefix=WARN14 %s
// WARN14: warning: overriding '-ffp-model=precise' option with '-ffp-contract=off' [-Woverriding-option]

// RUN: %clang -### -ffp-model=precise -ffp-contract=fast -c %s 2>&1 \
// RUN: | FileCheck --check-prefix=WARN15 %s
// WARN15: warning: overriding '-ffp-model=precise' option with '-ffp-contract=fast' [-Woverriding-option]

// RUN: %clang -### -ffp-model=strict -fassociative-math -ffp-contract=on \
// RUN: -c %s 2>&1 | FileCheck --check-prefix=WARN16 %s
// WARN16: warning: overriding '-ffp-model=strict' option with '-fassociative-math' [-Woverriding-option]
// WARN16: warning: overriding '-ffp-model=strict' option with '-ffp-contract=on' [-Woverriding-option]


// RUN: %clang -### -c %s 2>&1 \
// RUN: | FileCheck --check-prefix=CHECK-NOROUND %s
// CHECK-NOROUND: "-cc1"
Expand Down