r331041 - [Driver, CodeGen] add options to enable/disable an FP cast optimization
Sanjay Patel via cfe-commits
cfe-commits at lists.llvm.org
Fri Apr 27 07:22:48 PDT 2018
Author: spatel
Date: Fri Apr 27 07:22:48 2018
New Revision: 331041
URL: http://llvm.org/viewvc/llvm-project?rev=331041&view=rev
Log:
[Driver, CodeGen] add options to enable/disable an FP cast optimization
As discussed in the post-commit thread for:
rL330437 ( http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20180423/545906.html )
We need a way to opt-out of a float-to-int-to-float cast optimization because too much
existing code relies on the platform-specific undefined result of those casts when the
float-to-int overflows.
The LLVM changes associated with adding this function attribute are here:
rL330947
rL330950
rL330951
Also as suggested, I changed the LLVM doc to mention the specific sanitizer flag that
catches this problem:
rL330958
Differential Revision: https://reviews.llvm.org/D46135
Added:
cfe/trunk/test/CodeGen/no-junk-ftrunc.c
Modified:
cfe/trunk/docs/UsersManual.rst
cfe/trunk/include/clang/Driver/Options.td
cfe/trunk/include/clang/Frontend/CodeGenOptions.def
cfe/trunk/lib/CodeGen/CGCall.cpp
cfe/trunk/lib/Driver/ToolChains/Clang.cpp
cfe/trunk/lib/Frontend/CompilerInvocation.cpp
cfe/trunk/test/Driver/fast-math.c
Modified: cfe/trunk/docs/UsersManual.rst
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/docs/UsersManual.rst?rev=331041&r1=331040&r2=331041&view=diff
==============================================================================
--- cfe/trunk/docs/UsersManual.rst (original)
+++ cfe/trunk/docs/UsersManual.rst Fri Apr 27 07:22:48 2018
@@ -1255,6 +1255,16 @@ are listed below.
flushed-to-zero number is preserved in the sign of 0, denormals are
flushed to positive zero, respectively.
+.. option:: -f[no-]fp-cast-overflow-workaround
+
+ Enable a workaround for code that casts floating-point values to
+ integers and back to floating-point. If the floating-point value
+ is not representable in the intermediate integer type, the code is
+ incorrect according to the language standard. This flag will attempt
+ to generate code as if the result of an overflowing conversion matches
+ the overflowing behavior of a target's native float-to-int conversion
+ instructions.
+
.. option:: -fwhole-program-vtables
Enable whole-program vtable optimizations, such as single-implementation
Modified: cfe/trunk/include/clang/Driver/Options.td
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Driver/Options.td?rev=331041&r1=331040&r2=331041&view=diff
==============================================================================
--- cfe/trunk/include/clang/Driver/Options.td (original)
+++ cfe/trunk/include/clang/Driver/Options.td Fri Apr 27 07:22:48 2018
@@ -1029,6 +1029,11 @@ def ffp_contract : Joined<["-"], "ffp-co
Flags<[CC1Option]>, HelpText<"Form fused FP ops (e.g. FMAs): fast (everywhere)"
" | on (according to FP_CONTRACT pragma, default) | off (never fuse)">, Values<"fast,on,off">;
+def ffp_cast_overflow_workaround : Flag<["-"],
+ "ffp-cast-overflow-workaround">, Group<f_Group>, Flags<[CC1Option]>;
+def fno_fp_cast_overflow_workaround : Flag<["-"],
+ "fno-fp-cast-overflow-workaround">, Group<f_Group>, Flags<[CC1Option]>;
+
def ffor_scope : Flag<["-"], "ffor-scope">, Group<f_Group>;
def fno_for_scope : Flag<["-"], "fno-for-scope">, Group<f_Group>;
Modified: cfe/trunk/include/clang/Frontend/CodeGenOptions.def
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Frontend/CodeGenOptions.def?rev=331041&r1=331040&r2=331041&view=diff
==============================================================================
--- cfe/trunk/include/clang/Frontend/CodeGenOptions.def (original)
+++ cfe/trunk/include/clang/Frontend/CodeGenOptions.def Fri Apr 27 07:22:48 2018
@@ -136,6 +136,12 @@ CODEGENOPT(NoTrappingMath , 1, 0) ///
CODEGENOPT(NoNaNsFPMath , 1, 0) ///< Assume FP arguments, results not NaN.
CODEGENOPT(FlushDenorm , 1, 0) ///< Allow FP denorm numbers to be flushed to zero
CODEGENOPT(CorrectlyRoundedDivSqrt, 1, 0) ///< -cl-fp32-correctly-rounded-divide-sqrt
+
+/// Disable a float-to-int-to-float cast optimization. This attempts to generate
+/// code as if the result of an overflowing conversion matches the overflowing
+/// behavior of a target's native float-to-int conversion instructions.
+CODEGENOPT(FPCastOverflowWorkaround, 1, 0)
+
CODEGENOPT(UniformWGSize , 1, 0) ///< -cl-uniform-work-group-size
CODEGENOPT(NoZeroInitializedInBSS , 1, 0) ///< -fno-zero-initialized-in-bss.
/// \brief Method of Objective-C dispatch to use.
Modified: cfe/trunk/lib/CodeGen/CGCall.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGCall.cpp?rev=331041&r1=331040&r2=331041&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CGCall.cpp (original)
+++ cfe/trunk/lib/CodeGen/CGCall.cpp Fri Apr 27 07:22:48 2018
@@ -1727,6 +1727,9 @@ void CodeGenModule::ConstructDefaultFnAt
FuncAttrs.addAttribute("no-trapping-math",
llvm::toStringRef(CodeGenOpts.NoTrappingMath));
+ if (CodeGenOpts.FPCastOverflowWorkaround)
+ FuncAttrs.addAttribute("fp-cast-overflow-workaround", "true");
+
// TODO: Are these all needed?
// unsafe/inf/nan/nsz are handled by instruction-level FastMathFlags.
FuncAttrs.addAttribute("no-infs-fp-math",
Modified: cfe/trunk/lib/Driver/ToolChains/Clang.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Driver/ToolChains/Clang.cpp?rev=331041&r1=331040&r2=331041&view=diff
==============================================================================
--- cfe/trunk/lib/Driver/ToolChains/Clang.cpp (original)
+++ cfe/trunk/lib/Driver/ToolChains/Clang.cpp Fri Apr 27 07:22:48 2018
@@ -2241,6 +2241,11 @@ static void RenderFloatingPointOptions(c
CmdArgs.push_back("-mfpmath");
CmdArgs.push_back(A->getValue());
}
+
+ // Disable a codegen optimization for floating-point casts.
+ if (Args.hasFlag(options::OPT_ffp_cast_overflow_workaround,
+ options::OPT_fno_fp_cast_overflow_workaround, false))
+ CmdArgs.push_back("-ffp-cast-overflow-workaround");
}
static void RenderAnalyzerOptions(const ArgList &Args, ArgStringList &CmdArgs,
Modified: cfe/trunk/lib/Frontend/CompilerInvocation.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Frontend/CompilerInvocation.cpp?rev=331041&r1=331040&r2=331041&view=diff
==============================================================================
--- cfe/trunk/lib/Frontend/CompilerInvocation.cpp (original)
+++ cfe/trunk/lib/Frontend/CompilerInvocation.cpp Fri Apr 27 07:22:48 2018
@@ -699,6 +699,8 @@ static bool ParseCodeGenArgs(CodeGenOpti
Opts.Reciprocals = Args.getAllArgValues(OPT_mrecip_EQ);
Opts.ReciprocalMath = Args.hasArg(OPT_freciprocal_math);
Opts.NoTrappingMath = Args.hasArg(OPT_fno_trapping_math);
+ Opts.FPCastOverflowWorkaround = Args.hasArg(OPT_ffp_cast_overflow_workaround);
+
Opts.NoZeroInitializedInBSS = Args.hasArg(OPT_mno_zero_initialized_in_bss);
Opts.NumRegisterParameters = getLastArgIntValue(Args, OPT_mregparm, 0, Diags);
Opts.NoExecStack = Args.hasArg(OPT_mno_exec_stack);
Added: cfe/trunk/test/CodeGen/no-junk-ftrunc.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/no-junk-ftrunc.c?rev=331041&view=auto
==============================================================================
--- cfe/trunk/test/CodeGen/no-junk-ftrunc.c (added)
+++ cfe/trunk/test/CodeGen/no-junk-ftrunc.c Fri Apr 27 07:22:48 2018
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -S -ffp-cast-overflow-workaround %s -emit-llvm -o - | FileCheck %s
+// CHECK-LABEL: main
+// CHECK: attributes #0 = {{.*}}"fp-cast-overflow-workaround"="true"{{.*}}
+
+// The workaround attribute is not applied by default.
+
+// RUN: %clang_cc1 -S %s -emit-llvm -o - | FileCheck %s --check-prefix=DEFAULT
+// DEFAULT-LABEL: main
+// DEFAULT-NOT: fp-cast-overflow-workaround
+
+int main() {
+ return 0;
+}
+
Modified: cfe/trunk/test/Driver/fast-math.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Driver/fast-math.c?rev=331041&r1=331040&r2=331041&view=diff
==============================================================================
--- cfe/trunk/test/Driver/fast-math.c (original)
+++ cfe/trunk/test/Driver/fast-math.c Fri Apr 27 07:22:48 2018
@@ -287,3 +287,27 @@
// RUN: %clang -### -ftrapping-math -fno-trapping-math -c %s 2>&1 \
// RUN: | FileCheck --check-prefix=CHECK-NO-TRAPPING-MATH %s
// CHECK-NO-TRAPPING-MATH: "-fno-trapping-math"
+
+// This isn't fast-math, but the option is handled in the same place as other FP params.
+// Last option wins, and the flag is *not* passed by default.
+
+// RUN: %clang -### -ffp-cast-overflow-workaround -c %s 2>&1 \
+// RUN: | FileCheck --check-prefix=CHECK-FPOV-WORKAROUND %s
+// CHECK-FPOV-WORKAROUND: "-cc1"
+// CHECK-FPOV-WORKAROUND: "-ffp-cast-overflow-workaround"
+
+// RUN: %clang -### -c %s 2>&1 \
+// RUN: | FileCheck --check-prefix=CHECK-FPOV-WORKAROUND-DEFAULT %s
+// CHECK-FPOV-WORKAROUND-DEFAULT: "-cc1"
+// CHECK-FPOV-WORKAROUND-DEFAULT-NOT: "-ffp-cast-overflow-workaround"
+
+// RUN: %clang -### -fno-fp-cast-overflow-workaround -c %s 2>&1 \
+// RUN: | FileCheck --check-prefix=CHECK-NO-FPOV-WORKAROUND %s
+// CHECK-NO-FPOV-WORKAROUND: "-cc1"
+// CHECK-NO-FPOV-WORKAROUND-NOT: "-ffp-cast-overflow-workaround"
+
+// RUN: %clang -### -ffp-cast-overflow-workaround -fno-fp-cast-overflow-workaround -c %s 2>&1 \
+// RUN: | FileCheck --check-prefix=CHECK-NO-FPOV-WORKAROUND-OVERRIDE %s
+// CHECK-NO-FPOV-WORKAROUND-OVERRIDE: "-cc1"
+// CHECK-NO-FPOV-WORKAROUND-OVERRIDE-NOT: "-ffp-cast-overflow-workaround"
+
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