[clang] 2ef7cbf - [clang] Add deprecation warning for `-Ofast` driver option (#98736)
via cfe-commits
cfe-commits at lists.llvm.org
Thu Jul 18 00:49:57 PDT 2024
Author: Vlad Serebrennikov
Date: 2024-07-18T11:49:53+04:00
New Revision: 2ef7cbf71c98246d6f3a9c63dea75b76c7b5e928
URL: https://github.com/llvm/llvm-project/commit/2ef7cbf71c98246d6f3a9c63dea75b76c7b5e928
DIFF: https://github.com/llvm/llvm-project/commit/2ef7cbf71c98246d6f3a9c63dea75b76c7b5e928.diff
LOG: [clang] Add deprecation warning for `-Ofast` driver option (#98736)
This patch implements consensus on the corresponding RFC documented
here: https://discourse.llvm.org/t/rfc-deprecate-ofast/78687/72
Specifically, I added a deprecation warning for `-Ofast`, that suggests
to use `-O3` or `-O3` with `-ffast-math`, and a new diagnostic group for
aforementioned warning.
Deprecation period is going to be lengthy, so I hope this PR can be
merged in time for Clang 19.
Added:
Modified:
clang/docs/CommandGuide/clang.rst
clang/docs/ReleaseNotes.rst
clang/include/clang/Basic/DiagnosticDriverKinds.td
clang/include/clang/Basic/DiagnosticGroups.td
clang/include/clang/Driver/Options.td
clang/lib/Driver/ToolChains/Clang.cpp
clang/test/Driver/Ofast.c
Removed:
################################################################################
diff --git a/clang/docs/CommandGuide/clang.rst b/clang/docs/CommandGuide/clang.rst
index 29154292dc7a5..663aca1f6ddcb 100644
--- a/clang/docs/CommandGuide/clang.rst
+++ b/clang/docs/CommandGuide/clang.rst
@@ -429,7 +429,8 @@ Code Generation Options
:option:`-Ofast` Enables all the optimizations from :option:`-O3` along
with other aggressive optimizations that may violate strict compliance with
- language standards.
+ language standards. This is deprecated in favor of :option:`-O3`
+ in combination with :option:`-ffast-math`.
:option:`-Os` Like :option:`-O2` with extra optimizations to reduce code
size.
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 1c1b874273a7c..469510d175887 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -473,6 +473,13 @@ New Compiler Flags
Deprecated Compiler Flags
-------------------------
+- The ``-Ofast`` command-line option has been deprecated. This option both
+ enables the ``-O3`` optimization-level, as well as enabling non-standard
+ ``-ffast-math`` behaviors. As such, it is somewhat misleading as an
+ "optimization level". Users are advised to switch to ``-O3 -ffast-math`` if
+ the use of non-standard math behavior is intended, and ``-O3`` otherwise.
+ See `RFC <https://discourse.llvm.org/t/rfc-deprecate-ofast/78687>`_ for details.
+
Modified Compiler Flags
-----------------------
- Added a new diagnostic flag ``-Wreturn-mismatch`` which is grouped under
diff --git a/clang/include/clang/Basic/DiagnosticDriverKinds.td b/clang/include/clang/Basic/DiagnosticDriverKinds.td
index 359c0de7f811c..cfa897f28b4c0 100644
--- a/clang/include/clang/Basic/DiagnosticDriverKinds.td
+++ b/clang/include/clang/Basic/DiagnosticDriverKinds.td
@@ -442,6 +442,10 @@ def warn_drv_deprecated_arg : Warning<
def warn_drv_deprecated_arg_no_relaxed_template_template_args : Warning<
"argument '-fno-relaxed-template-template-args' is deprecated">,
InGroup<DeprecatedNoRelaxedTemplateTemplateArgs>;
+def warn_drv_deprecated_arg_ofast : Warning<
+ "argument '-Ofast' is deprecated; use '-O3 -ffast math' for the same behavior,"
+ " or '-O3' to enable only conforming optimizations">,
+ InGroup<DeprecatedOFast>;
def warn_drv_deprecated_custom : Warning<
"argument '%0' is deprecated, %1">, InGroup<Deprecated>;
def warn_drv_assuming_mfloat_abi_is : Warning<
diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 2241f8481484e..d7dba76a0fcf8 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -103,6 +103,7 @@ def EnumConversion : DiagGroup<"enum-conversion",
EnumFloatConversion,
EnumCompareConditional]>;
def DeprecatedNoRelaxedTemplateTemplateArgs : DiagGroup<"deprecated-no-relaxed-template-template-args">;
+def DeprecatedOFast : DiagGroup<"deprecated-ofast">;
def ObjCSignedCharBoolImplicitIntConversion :
DiagGroup<"objc-signed-char-bool-implicit-int-conversion">;
def Shorten64To32 : DiagGroup<"shorten-64-to-32">;
@@ -228,6 +229,7 @@ def Deprecated : DiagGroup<"deprecated", [DeprecatedAnonEnumEnumConversion,
DeprecatedPragma,
DeprecatedRegister,
DeprecatedNoRelaxedTemplateTemplateArgs,
+ DeprecatedOFast,
DeprecatedThisCapture,
DeprecatedType,
DeprecatedVolatile,
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 25555e4620523..1675e435d210c 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -931,7 +931,9 @@ def O : Joined<["-"], "O">, Group<O_Group>,
def O_flag : Flag<["-"], "O">, Visibility<[ClangOption, CC1Option, FC1Option]>,
Alias<O>, AliasArgs<["1"]>;
def Ofast : Joined<["-"], "Ofast">, Group<O_Group>,
- Visibility<[ClangOption, CC1Option, FlangOption]>;
+ Visibility<[ClangOption, CC1Option, FlangOption]>,
+ HelpText<"Deprecated; use '-O3 -ffast math' for the same behavior,"
+ " or '-O3' to enable only conforming optimizations">;
def P : Flag<["-"], "P">,
Visibility<[ClangOption, CC1Option, FlangOption, FC1Option]>,
Group<Preprocessor_Group>,
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index a8a7cef09972e..1fd6fba210042 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -5725,6 +5725,8 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
options::OPT_fno_zero_initialized_in_bss);
bool OFastEnabled = isOptimizationLevelFast(Args);
+ if (OFastEnabled)
+ D.Diag(diag::warn_drv_deprecated_arg_ofast);
// If -Ofast is the optimization level, then -fstrict-aliasing should be
// enabled. This alias option is being used to simplify the hasFlag logic.
OptSpecifier StrictAliasingAliasOption =
diff --git a/clang/test/Driver/Ofast.c b/clang/test/Driver/Ofast.c
index 8b7f2217eca2f..4c63caf9865d5 100644
--- a/clang/test/Driver/Ofast.c
+++ b/clang/test/Driver/Ofast.c
@@ -3,19 +3,21 @@
// RUN: %clang -fno-fast-math -Ofast -### %s 2>&1 | FileCheck -check-prefix=CHECK-OFAST %s
// RUN: %clang -fno-strict-aliasing -Ofast -### %s 2>&1 | FileCheck -check-prefix=CHECK-OFAST %s
// RUN: %clang -fno-vectorize -Ofast -### %s 2>&1 | FileCheck -check-prefix=CHECK-OFAST %s
-// RUN: %clang -Ofast -O2 -### %s 2>&1 | FileCheck -check-prefix=CHECK-OFAST-O2 \
+// RUN: %clang -Ofast -O2 -### -Werror %s 2>&1 | FileCheck -check-prefix=CHECK-OFAST-O2 \
// RUN: %if target={{.*-windows-msvc.*}} %{ --check-prefix=CHECK-OFAST-O2-ALIASING-MSVC %} \
// RUN: %else %{ --check-prefix=CHECK-OFAST-O2-ALIASING %} %s
// RUN: %clang -Ofast -fno-fast-math -### %s 2>&1 | FileCheck -check-prefix=CHECK-OFAST-NO-FAST-MATH %s
// RUN: %clang -Ofast -fno-strict-aliasing -### %s 2>&1 | FileCheck -check-prefix=CHECK-OFAST-NO-STRICT-ALIASING %s
// RUN: %clang -Ofast -fno-vectorize -### %s 2>&1 | FileCheck -check-prefix=CHECK-OFAST-NO-VECTORIZE %s
+// CHECK-OFAST: use '-O3 -ffast math' for the same behavior, or '-O3' to enable only conforming optimizations
// CHECK-OFAST: -cc1
// CHECK-OFAST-NOT: -relaxed-aliasing
// CHECK-OFAST: -ffast-math
// CHECK-OFAST: -Ofast
// CHECK-OFAST: -vectorize-loops
+// Lack of warning about '-Ofast' deprecation is checked via -Werror
// CHECK-OFAST-O2: -cc1
// CHECK-OFAST-O2-ALIASING-NOT: -relaxed-aliasing
// CHECK-OFAST-O2-ALIASING-MSVC: -relaxed-aliasing
@@ -23,18 +25,21 @@
// CHECK-OFAST-O2-NOT: -Ofast
// CHECK-OFAST-O2: -vectorize-loops
+// CHECK-OFAST-NO-FAST-MATH: use '-O3 -ffast math' for the same behavior, or '-O3' to enable only conforming optimizations
// CHECK-OFAST-NO-FAST-MATH: -cc1
// CHECK-OFAST-NO-FAST-MATH-NOT: -relaxed-aliasing
// CHECK-OFAST-NO-FAST-MATH-NOT: -ffast-math
// CHECK-OFAST-NO-FAST-MATH: -Ofast
// CHECK-OFAST-NO-FAST-MATH: -vectorize-loops
+// CHECK-OFAST-NO-STRICT-ALIASING: use '-O3 -ffast math' for the same behavior, or '-O3' to enable only conforming optimizations
// CHECK-OFAST-NO-STRICT-ALIASING: -cc1
// CHECK-OFAST-NO-STRICT-ALIASING: -relaxed-aliasing
// CHECK-OFAST-NO-STRICT-ALIASING: -ffast-math
// CHECK-OFAST-NO-STRICT-ALIASING: -Ofast
// CHECK-OFAST-NO-STRICT-ALIASING: -vectorize-loops
+// CHECK-OFAST-NO-VECTORIZE: use '-O3 -ffast math' for the same behavior, or '-O3' to enable only conforming optimizations
// CHECK-OFAST-NO-VECTORIZE: -cc1
// CHECK-OFAST-NO-VECTORIZE-NOT: -relaxed-aliasing
// CHECK-OFAST-NO-VECTORIZE: -ffast-math
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