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[flang][driver] Add options -fdefault-integer-4 and -fdefault-real-4 #172323

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tarunprabhu merged 2 commits into from
Dec 16, 2025
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[flang][driver] Add options -fdefault-integer-4 and -fdefault-real-4 #172323

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[flang][driver] Add options -fdefault-integer-4 and -fdefault-real-4
tarunprabhu Dec 15, 2025
e0c5288
Merge branch 'main' into add-default-4
tarunprabhu Dec 16, 2025
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4 changes: 4 additions & 0 deletions clang/include/clang/Options/Options.td
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Expand Up @@ -7348,6 +7348,10 @@ def fdefault_integer_8 : Flag<["-"],"fdefault-integer-8">, Group<f_Group>,
HelpText<"Set the default integer and logical kind to an 8 byte wide type">;
def fdefault_real_8 : Flag<["-"],"fdefault-real-8">, Group<f_Group>,
HelpText<"Set the default real kind to an 8 byte wide type">;
def fdefault_integer_4 : Flag<["-"],"fdefault-integer-4">, Group<f_Group>,
HelpText<"Set the default integer and logical kind to a 4 byte wide type">;
def fdefault_real_4 : Flag<["-"],"fdefault-real-4">, Group<f_Group>,
HelpText<"Set the default real kind to a 4 byte wide type">;
def fdisable_real_3 : Flag<["-"],"fdisable-real-3">, Group<f_Group>,
HelpText<"Disable real(KIND=3) from TargetCharacteristics">, Flags<[HelpHidden]>;
def fdisable_real_10 : Flag<["-"],"fdisable-real-10">, Group<f_Group>,
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2 changes: 2 additions & 0 deletions clang/lib/Driver/ToolChains/Flang.cpp
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Expand Up @@ -51,6 +51,8 @@ void Flang::addFortranDialectOptions(const ArgList &Args,
options::OPT_fxor_operator,
options::OPT_fno_xor_operator,
options::OPT_falternative_parameter_statement,
options::OPT_fdefault_integer_4,
options::OPT_fdefault_real_4,
options::OPT_fdefault_real_8,
options::OPT_fdefault_integer_8,
options::OPT_fdefault_double_8,
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36 changes: 28 additions & 8 deletions flang/lib/Frontend/CompilerInvocation.cpp
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Expand Up @@ -1086,15 +1086,35 @@ static bool parseDialectArgs(CompilerInvocation &res, llvm::opt::ArgList &args,
}

// -fdefault* family
if (args.hasArg(clang::options::OPT_fdefault_real_8)) {
res.getDefaultKinds().set_defaultRealKind(8);
res.getDefaultKinds().set_doublePrecisionKind(16);
if (const llvm::opt::Arg *arg =
args.getLastArg(clang::options::OPT_fdefault_real_8,
clang::options::OPT_fdefault_real_4)) {
const llvm::opt::Option &opt = arg->getOption();
if (opt.matches(clang::options::OPT_fdefault_real_8)) {
res.getDefaultKinds().set_defaultRealKind(8);
res.getDefaultKinds().set_doublePrecisionKind(16);
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@eugeneepshteyn eugeneepshteyn Dec 16, 2025

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Hmm, what if the target platform doesn't support real16?

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@tarunprabhu tarunprabhu Dec 16, 2025

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There PR does not change the behavior of -fdefault-real-8, so flang will continue to behave as it would have before.

program test
  implicit none
  double precision :: n

  write(*,*) acos(n)
end program test

If I compile the code above on a machine without support for real(16), I get this:

flang -fdefault-real-8 -o /tmp/a.out -O2 /tmp/test.f90 && /tmp/a.out
/usr/bin/ld: /tmp/double-0c6305.o: in function `_QQmain':
FIRModule:(.text+0x1f): undefined reference to `_FortranAAcosF128'
/usr/bin/ld: /tmp/double-0c6305.o: in function `main':
FIRModule:(.text+0x96): undefined reference to `_FortranAAcosF128'

It may be a better user experience to emit a warning - or even an error - -fdefault-real-8 is used on a target that does not support real(16). IMO, that is an unrelated change that should be deferred to a different PR.

} else if (opt.matches(clang::options::OPT_fdefault_real_4)) {
res.getDefaultKinds().set_defaultRealKind(4);
res.getDefaultKinds().set_doublePrecisionKind(8);
}
}
if (args.hasArg(clang::options::OPT_fdefault_integer_8)) {
res.getDefaultKinds().set_defaultIntegerKind(8);
res.getDefaultKinds().set_subscriptIntegerKind(8);
res.getDefaultKinds().set_sizeIntegerKind(8);
res.getDefaultKinds().set_defaultLogicalKind(8);
if (const llvm::opt::Arg *arg =
args.getLastArg(clang::options::OPT_fdefault_integer_8,
clang::options::OPT_fdefault_integer_4)) {
const llvm::opt::Option &opt = arg->getOption();
if (opt.matches(clang::options::OPT_fdefault_integer_8)) {
res.getDefaultKinds().set_defaultIntegerKind(8);
res.getDefaultKinds().set_subscriptIntegerKind(8);
res.getDefaultKinds().set_sizeIntegerKind(8);
res.getDefaultKinds().set_defaultLogicalKind(8);
} else if (opt.matches(clang::options::OPT_fdefault_integer_4)) {
// Note that the subscript integer kind is set to 8 here. If a
// default-integer-kind is not provided, it is also set to 8.
res.getDefaultKinds().set_defaultIntegerKind(4);
res.getDefaultKinds().set_subscriptIntegerKind(8);
res.getDefaultKinds().set_sizeIntegerKind(4);
res.getDefaultKinds().set_defaultLogicalKind(4);
}
}
if (args.hasArg(clang::options::OPT_fdefault_double_8)) {
if (!args.hasArg(clang::options::OPT_fdefault_real_8)) {
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130 changes: 99 additions & 31 deletions flang/test/Driver/fdefault.f90
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@@ -1,46 +1,114 @@
! Ensure argument -fdefault* work as expected.
! TODO: Add checks when actual codegen is possible for this family

!--------------------------
! FLANG DRIVER (flang)
!--------------------------
! RUN: rm -rf %t/dir-flang && mkdir -p %t/dir-flang && %flang -fsyntax-only -module-dir %t/dir-flang %s 2>&1
! RUN: cat %t/dir-flang/m.mod | FileCheck %s --check-prefix=NOOPTION
! RUN: rm -rf %t/dir-flang && mkdir -p %t/dir-flang && %flang -fsyntax-only -fdefault-real-8 -module-dir %t/dir-flang %s 2>&1
! RUN: cat %t/dir-flang/m.mod | FileCheck %s --check-prefix=REAL8
! RUN: rm -rf %t/dir-flang && mkdir -p %t/dir-flang && %flang -fsyntax-only -fdefault-real-8 -fdefault-double-8 -module-dir %t/dir-flang %s 2>&1
! RUN: cat %t/dir-flang/m.mod | FileCheck %s --check-prefix=DOUBLE8
! RUN: not %flang -fsyntax-only -fdefault-double-8 %s 2>&1 | FileCheck %s --check-prefix=ERROR

!-----------------------------------------
! FRONTEND FLANG DRIVER (flang -fc1)
!-----------------------------------------
! RUN: rm -rf %t/dir-flang && mkdir -p %t/dir-flang && %flang_fc1 -fsyntax-only -module-dir %t/dir-flang %s 2>&1
! RUN: cat %t/dir-flang/m.mod | FileCheck %s --check-prefix=NOOPTION
! RUN: rm -rf %t/dir-flang && mkdir -p %t/dir-flang && %flang_fc1 -fsyntax-only -fdefault-real-8 -module-dir %t/dir-flang %s 2>&1
! RUN: cat %t/dir-flang/m.mod | FileCheck %s --check-prefix=REAL8
! RUN: rm -rf %t/dir-flang && mkdir -p %t/dir-flang && %flang_fc1 -fsyntax-only -fdefault-real-8 -fdefault-double-8 -module-dir %t/dir-flang %s 2>&1
! RUN: cat %t/dir-flang/m.mod | FileCheck %s --check-prefix=DOUBLE8
! RUN: not %flang_fc1 -fsyntax-only -fdefault-double-8 %s 2>&1 | FileCheck %s --check-prefix=ERROR

! NOOPTION: integer(4),parameter::real_kind=4_4
!
! RUN: rm -rf %t && mkdir -p %t && \
! RUN: %flang_fc1 -fsyntax-only -module-dir %t %s
! RUN: cat %t/m.mod | FileCheck %s --check-prefix=NOOPTION
!
! RUN: rm -rf %t && mkdir -p %t && \
! RUN: %flang_fc1 -fsyntax-only -fdefault-integer-4 -module-dir %t %s
! RUN: cat %t/m.mod | FileCheck %s --check-prefix=INTEGER4
!
! RUN: rm -rf %t && mkdir -p %t && \
! RUN: %flang_fc1 -fsyntax-only -fdefault-real-4 -module-dir %t %s
! RUN: cat %t/m.mod | FileCheck %s --check-prefix=REAL4
!
! RUN: rm -rf %t && mkdir -p %t && \
! RUN: %flang_fc1 -fsyntax-only -fdefault-integer-4 -fdefault-real-4 \
! RUN: -module-dir %t %s
! RUN: cat %t/m.mod | FileCheck %s --check-prefix=BOTH4
!
! RUN: rm -rf %t && mkdir -p %t && \
! RUN: %flang_fc1 -fsyntax-only -fdefault-integer-8 -module-dir %t %s
! RUN: cat %t/m.mod | FileCheck %s --check-prefix=INTEGER8
!
! RUN: rm -rf %t && mkdir -p %t && \
! RUN: %flang -fsyntax-only -fdefault-real-8 -module-dir %t %s
! RUN: cat %t/m.mod | FileCheck %s --check-prefix=REAL8
!
! RUN: rm -rf %t && mkdir -p %t && \
! RUN: %flang_fc1 -fsyntax-only -fdefault-integer-8 -fdefault-real-8 \
! RUN: -module-dir %t %s
! RUN: cat %t/m.mod | FileCheck %s --check-prefix=BOTH8
!
! RUN: rm -rf %t && mkdir -p %t && \
! RUN: %flang_fc1 -fsyntax-only -fdefault-real-8 -fdefault-double-8 \
! RUN: -module-dir %t %s
! RUN: cat %t/m.mod | FileCheck %s --check-prefix=DOUBLE8
!
! RUN: not %flang_fc1 -fsyntax-only -fdefault-double-8 %s 2>&1 \
! RUN: | FileCheck %s --check-prefix=ERROR
!
! The last occurrence of -fdefault-* "wins"
!
! RUN: rm -rf %t && mkdir -p %t && \
! RUN: %flang_fc1 -fsyntax-only -fdefault-integer-4 -fdefault-integer-8 \
! RUN: -module-dir %t %s
! RUN: cat %t/m.mod | FileCheck %s --check-prefix=INTEGER8
!
! RUN: rm -rf %t && mkdir -p %t && \
! RUN: %flang_fc1 -fsyntax-only -fdefault-integer-8 -fdefault-integer-4 \
! RUN: -module-dir %t %s
! RUN: cat %t/m.mod | FileCheck %s --check-prefix=INTEGER4
!
! RUN: rm -rf %t && mkdir -p %t && \
! RUN: %flang_fc1 -fsyntax-only -fdefault-real-4 -fdefault-real-8 \
! RUN: -module-dir %t %s
! RUN: cat %t/m.mod | FileCheck %s --check-prefix=REAL8
!
! RUN: rm -rf %t && mkdir -p %t && \
! RUN: %flang_fc1 -fsyntax-only -fdefault-real-8 -fdefault-real-4 \
! RUN: -module-dir %t %s
! RUN: cat %t/m.mod | FileCheck %s --check-prefix=REAL4
!
! NOOPTION: integer(4),parameter::integer_kind=4_4
! NOOPTION-NEXT: intrinsic::kind
! NOOPTION-NEXT: integer(4),parameter::real_kind=4_4
! NOOPTION-NEXT: integer(4),parameter::double_kind=8_4

! REAL8: integer(4),parameter::real_kind=8_4
!
! INTEGER4: integer(4),parameter::integer_kind=4_4
! INTEGER4-NEXT: intrinsic::kind
! INTEGER4-NEXT: integer(4),parameter::real_kind=4_4
! INTEGER4-NEXT: integer(4),parameter::double_kind=8_4
!
! REAL4: integer(4),parameter::integer_kind=4_4
! REAL4-NEXT: intrinsic::kind
! REAL4-NEXT: integer(4),parameter::real_kind=4_4
! REAL4-NEXT: integer(4),parameter::double_kind=8_4
!
! BOTH4: integer(4),parameter::integer_kind=4_4
! BOTH4-NEXT: intrinsic::kind
! BOTH4-NEXT: integer(4),parameter::real_kind=4_4
! BOTH4-NEXT: integer(4),parameter::double_kind=8_4
!
! INTEGER8: integer(8),parameter::integer_kind=8_8
! INTEGER8-NEXT: intrinsic::kind
! INTEGER8-NEXT: integer(8),parameter::real_kind=4_8
! INTEGER8-NEXT: integer(8),parameter::double_kind=8_8
!
! REAL8: integer(4),parameter::integer_kind=4_4
! REAL8-NEXT: intrinsic::kind
! REAL8-NEXT: integer(4),parameter::real_kind=8_4
! REAL8-NEXT: integer(4),parameter::double_kind=16_4

! DOUBLE8: integer(4),parameter::real_kind=8_4
!
! BOTH8: integer(8),parameter::integer_kind=8_8
! BOTH8-NEXT: intrinsic::kind
! BOTH8-NEXT: integer(8),parameter::real_kind=8_8
! BOTH8-NEXT: integer(8),parameter::double_kind=16_8
!
! DOUBLE8: integer(4),parameter::integer_kind=4_4
! DOUBLE8-NEXT: intrinsic::kind
! DOUBLE8-NEXT: integer(4),parameter::real_kind=8_4
! DOUBLE8-NEXT: integer(4),parameter::double_kind=8_4

!
! ERROR: Use of `-fdefault-double-8` requires `-fdefault-real-8`

module m
implicit none
integer :: i
real :: x
double precision :: y
integer, parameter :: real_kind = kind(x) !-fdefault-real-8
integer, parameter :: double_kind = kind(y) !-fdefault-double-8
integer, parameter :: integer_kind = kind(i) !-fdefault-integer-*
integer, parameter :: real_kind = kind(x) !-fdefault-real-*
integer, parameter :: double_kind = kind(y) !-fdefault-double-*
end
4 changes: 4 additions & 0 deletions flang/test/Driver/frontend-forwarding.f90
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Expand Up @@ -3,6 +3,8 @@

! RUN: %flang -fsyntax-only -### %s -o %t 2>&1 \
! RUN: -finput-charset=utf-8 \
! RUN: -fdefault-integer-4 \
! RUN: -fdefault-real-4 \
! RUN: -fdefault-double-8 \
! RUN: -fdefault-integer-8 \
! RUN: -fdefault-real-8 \
Expand Down Expand Up @@ -35,6 +37,8 @@

! CHECK: "-P"
! CHECK: "-finput-charset=utf-8"
! CHECK: "-fdefault-integer-4"
! CHECK: "-fdefault-real-4"
! CHECK: "-fdefault-double-8"
! CHECK: "-fdefault-integer-8"
! CHECK: "-fdefault-real-8"
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18 changes: 18 additions & 0 deletions flang/test/Semantics/numeric_storage_size.f90
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@@ -1,4 +1,7 @@
! RUN: %flang_fc1 -fdebug-unparse %s 2>&1 | FileCheck %s --check-prefix=CHECK
! RUN: %flang_fc1 -fdebug-unparse -fdefault-integer-4 %s 2>&1 | FileCheck %s --check-prefix=CHECK-I4
! RUN: %flang_fc1 -fdebug-unparse %s -fdefault-real-4 2>&1 | FileCheck %s --check-prefix=CHECK-R4
! RUN: %flang_fc1 -fdebug-unparse %s -fdefault-integer-4 -fdefault-real-4 2>&1 | FileCheck %s --check-prefix=CHECK-I4-R4
! RUN: %flang_fc1 -fdebug-unparse -fdefault-integer-8 %s 2>&1 | FileCheck %s --check-prefix=CHECK-I8
! RUN: %flang_fc1 -fdebug-unparse %s -fdefault-real-8 2>&1 | FileCheck %s --check-prefix=CHECK-R8
! RUN: %flang_fc1 -fdebug-unparse %s -fdefault-integer-8 -fdefault-real-8 2>&1 | FileCheck %s --check-prefix=CHECK-I8-R8
Expand All @@ -7,6 +10,9 @@

!CHECK-NOT: warning
!CHECK: nss = 32_4
!CHECK-I4: nss = 32_4
!CHECK-R4: nss = 32_4
!CHECK-I4-R4: nss = 32_4
!CHECK-I8: warning: NUMERIC_STORAGE_SIZE from ISO_FORTRAN_ENV is not well-defined when default INTEGER and REAL are not consistent due to compiler options
!CHECK-I8: nss = 32_4
!CHECK-R8: warning: NUMERIC_STORAGE_SIZE from ISO_FORTRAN_ENV is not well-defined when default INTEGER and REAL are not consistent due to compiler options
Expand All @@ -15,24 +21,36 @@
integer, parameter :: nss = numeric_storage_size

!CHECK: iss = 32_4
!CHECK-I4: iss = 32_4
!CHECK-R4: iss = 32_4
!CHECK-I4-R4: iss = 32_4
!CHECK-I8: iss = 64_8
!CHECK-R8: iss = 32_4
!CHECK-I8-R8: iss = 64_8
integer, parameter :: iss = storage_size(1)

!CHECK: rss = 32_4
!CHECK-I4: rss = 32_4
!CHECK-R4: rss = 32_4
!CHECK-I4-R4: rss = 32_4
!CHECK-I8: rss = 32_8
!CHECK-R8: rss = 64_4
!CHECK-I8-R8: rss = 64_8
integer, parameter :: rss = storage_size(1.)

!CHECK: zss = 64_4
!CHECK-I4: zss = 64_4
!CHECK-R4: zss = 64_4
!CHECK-I4-R4: zss = 64_4
!CHECK-I8: zss = 64_8
!CHECK-R8: zss = 128_4
!CHECK-I8-R8: zss = 128_8
integer, parameter :: zss = storage_size((1.,0.))

!CHECK: lss = 32_4
!CHECK-I4: lss = 32_4
!CHECK-R4: lss = 32_4
!CHECK-I4-R4: lss = 32_4
!CHECK-I8: lss = 64_8
!CHECK-R8: lss = 32_4
!CHECK-I8-R8: lss = 64_8
Expand Down