[PATCH] D69979: clang: Guess at some platform FTZ/DAZ default settings

[Matt Arsenault via Phabricator via cfe-commits]

arsenm closed this revision.
arsenm added a comment.

fa7cd549d604bfd8f9dce5d649a19720cbc39cca 



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[PATCH] D69979: clang: Guess at some platform FTZ/DAZ default settings

[Sanjay Patel via Phabricator via cfe-commits]

spatel accepted this revision.
spatel added a comment.
This revision is now accepted and ready to land.

LGTM - the PS4 behavior was confirmed off-list.


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[PATCH] D69979: clang: Guess at some platform FTZ/DAZ default settings

[Matt Arsenault via Phabricator via cfe-commits]

arsenm updated this revision to Diff 243553.
arsenm added a comment.

Rebase and fix check prefix name


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Files:
  clang/include/clang/Driver/ToolChain.h
  clang/lib/Driver/ToolChain.cpp
  clang/lib/Driver/ToolChains/Gnu.cpp
  clang/lib/Driver/ToolChains/Linux.cpp
  clang/lib/Driver/ToolChains/Linux.h
  clang/lib/Driver/ToolChains/MinGW.cpp
  clang/lib/Driver/ToolChains/PS4CPU.h
  clang/test/Driver/default-denormal-fp-math.c

Index: clang/test/Driver/default-denormal-fp-math.c
===
--- /dev/null
+++ clang/test/Driver/default-denormal-fp-math.c
@@ -0,0 +1,19 @@
+// RUN: %clang -### -target arm-unknown-linux-gnu -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
+// RUN: %clang -### -target i386-unknown-linux-gnu -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
+
+// RUN: %clang -### -target x86_64-unknown-linux-gnu --sysroot=%S/Inputs/basic_linux_tree -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
+
+// crtfastmath enables ftz and daz
+// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffast-math --sysroot=%S/Inputs/basic_linux_tree -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-PRESERVESIGN %s
+
+// crt not linked in with nostartfiles
+// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffast-math -nostartfiles --sysroot=%S/Inputs/basic_linux_tree -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
+
+// If there's no crtfastmath, don't assume ftz/daz
+// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffast-math --sysroot=/dev/null -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
+
+// RUN: %clang -### -target x86_64-scei-ps4 -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-PRESERVESIGN %s
+
+
+// CHECK-IEEE: -fdenormal-fp-math=ieee,ieee
+// CHECK-PRESERVESIGN: -fdenormal-fp-math=preserve-sign,preserve-sign
Index: clang/lib/Driver/ToolChains/PS4CPU.h
===
--- clang/lib/Driver/ToolChains/PS4CPU.h
+++ clang/lib/Driver/ToolChains/PS4CPU.h
@@ -88,6 +88,14 @@
   // capable of unit splitting.
   bool canSplitThinLTOUnit() const override { return false; }
 
+  llvm::DenormalMode getDefaultDenormalModeForType(
+const llvm::opt::ArgList ,
+Action::OffloadKind DeviceOffloadKind,
+const llvm::fltSemantics *FPType) const override {
+// DAZ and FTZ are on by default.
+return llvm::DenormalMode::getPreserveSign();
+  }
+
 protected:
   Tool *buildAssembler() const override;
   Tool *buildLinker() const override;
Index: clang/lib/Driver/ToolChains/MinGW.cpp
===
--- clang/lib/Driver/ToolChains/MinGW.cpp
+++ clang/lib/Driver/ToolChains/MinGW.cpp
@@ -300,7 +300,7 @@
 
 if (!Args.hasArg(options::OPT_nostartfiles)) {
   // Add crtfastmath.o if available and fast math is enabled.
-  TC.AddFastMathRuntimeIfAvailable(Args, CmdArgs);
+  TC.addFastMathRuntimeIfAvailable(Args, CmdArgs);
 
   CmdArgs.push_back(Args.MakeArgString(TC.GetFilePath("crtend.o")));
 }
Index: clang/lib/Driver/ToolChains/Linux.h
===
--- clang/lib/Driver/ToolChains/Linux.h
+++ clang/lib/Driver/ToolChains/Linux.h
@@ -46,6 +46,11 @@
 
   std::vector ExtraOpts;
 
+  llvm::DenormalMode getDefaultDenormalModeForType(
+const llvm::opt::ArgList ,
+Action::OffloadKind DeviceOffloadKind,
+const llvm::fltSemantics *FPType = nullptr) const override;
+
 protected:
   Tool *buildAssembler() const override;
   Tool *buildLinker() const override;
Index: clang/lib/Driver/ToolChains/Linux.cpp
===
--- clang/lib/Driver/ToolChains/Linux.cpp
+++ clang/lib/Driver/ToolChains/Linux.cpp
@@ -988,3 +988,22 @@
 Twine("-u", llvm::getInstrProfRuntimeHookVarName(;
   ToolChain::addProfileRTLibs(Args, CmdArgs);
 }
+
+llvm::DenormalMode Linux::getDefaultDenormalModeForType(
+  const llvm::opt::ArgList ,
+  Action::OffloadKind DeviceOffloadKind,
+  const llvm::fltSemantics *FPType) const {
+  switch (getTriple().getArch()) {
+  case llvm::Triple::x86:
+  case llvm::Triple::x86_64: {
+std::string Unused;
+// DAZ and FTZ are turned on in crtfastmath.o
+if (!DriverArgs.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles) &&
+isFastMathRuntimeAvailable(DriverArgs, Unused))
+  return llvm::DenormalMode::getPreserveSign();
+return llvm::DenormalMode::getIEEE();
+  }
+  default:
+return llvm::DenormalMode::getIEEE();
+  }
+}
Index: clang/lib/Driver/ToolChains/Gnu.cpp
===
--- clang/lib/Driver/ToolChains/Gnu.cpp
+++ clang/lib/Driver/ToolChains/Gnu.cpp
@@ -502,7 +502,7 @@
 }
 
 // Add crtfastmath.o if available and fast math is enabled.
-ToolChain.AddFastMathRuntimeIfAvailable(Args, 

[PATCH] D69979: clang: Guess at some platform FTZ/DAZ default settings

[Sanjay Patel via Phabricator via cfe-commits]

spatel added inline comments.



Comment at: clang/test/Driver/default-denormal-fp-math.c:7
+// crtfastmath enables ftz and daz
+// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffast-math 
--sysroot=%S/Inputs/basic_linux_tree -c %s -v 2>&1 | FileCheck 
-check-prefix=CHECK-ZEROSIGN %s
+

The prefix should be PRESERVE_SIGN to match the flag?


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[PATCH] D69979: clang: Guess at some platform FTZ/DAZ default settings

[Matt Arsenault via Phabricator via cfe-commits]

arsenm added a comment.

ping


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[PATCH] D69979: clang: Guess at some platform FTZ/DAZ default settings

[Matt Arsenault via Phabricator via cfe-commits]

arsenm updated this revision to Diff 232088.
arsenm added a comment.

Rename functions


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Files:
  clang/include/clang/Driver/ToolChain.h
  clang/lib/Driver/ToolChain.cpp
  clang/lib/Driver/ToolChains/Gnu.cpp
  clang/lib/Driver/ToolChains/Linux.cpp
  clang/lib/Driver/ToolChains/Linux.h
  clang/lib/Driver/ToolChains/MinGW.cpp
  clang/lib/Driver/ToolChains/PS4CPU.h
  clang/test/Driver/default-denormal-fp-math.c

Index: clang/test/Driver/default-denormal-fp-math.c
===
--- /dev/null
+++ clang/test/Driver/default-denormal-fp-math.c
@@ -0,0 +1,19 @@
+// RUN: %clang -### -target arm-unknown-linux-gnu -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
+// RUN: %clang -### -target i386-unknown-linux-gnu -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
+
+// RUN: %clang -### -target x86_64-unknown-linux-gnu --sysroot=%S/Inputs/basic_linux_tree -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
+
+// crtfastmath enables ftz and daz
+// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffast-math --sysroot=%S/Inputs/basic_linux_tree -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-ZEROSIGN %s
+
+// crt not linked in with nostartfiles
+// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffast-math -nostartfiles --sysroot=%S/Inputs/basic_linux_tree -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
+
+// If there's no crtfastmath, don't assume ftz/daz
+// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffast-math --sysroot=/dev/null -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
+
+// RUN: %clang -### -target x86_64-scei-ps4 -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-ZEROSIGN %s
+
+
+// CHECK-IEEE: -fdenormal-fp-math=ieee,ieee
+// CHECK-ZEROSIGN: -fdenormal-fp-math=preserve-sign,preserve-sign
Index: clang/lib/Driver/ToolChains/PS4CPU.h
===
--- clang/lib/Driver/ToolChains/PS4CPU.h
+++ clang/lib/Driver/ToolChains/PS4CPU.h
@@ -88,6 +88,14 @@
   // capable of unit splitting.
   bool canSplitThinLTOUnit() const override { return false; }
 
+  llvm::DenormalMode getDefaultDenormalModeForType(
+const llvm::opt::ArgList ,
+Action::OffloadKind DeviceOffloadKind,
+const llvm::fltSemantics *FPType) const override {
+// DAZ and FTZ are on by default.
+return llvm::DenormalMode::getPreserveSign();
+  }
+
 protected:
   Tool *buildAssembler() const override;
   Tool *buildLinker() const override;
Index: clang/lib/Driver/ToolChains/MinGW.cpp
===
--- clang/lib/Driver/ToolChains/MinGW.cpp
+++ clang/lib/Driver/ToolChains/MinGW.cpp
@@ -288,7 +288,7 @@
 
 if (!Args.hasArg(options::OPT_nostartfiles)) {
   // Add crtfastmath.o if available and fast math is enabled.
-  TC.AddFastMathRuntimeIfAvailable(Args, CmdArgs);
+  TC.addFastMathRuntimeIfAvailable(Args, CmdArgs);
 
   CmdArgs.push_back(Args.MakeArgString(TC.GetFilePath("crtend.o")));
 }
Index: clang/lib/Driver/ToolChains/Linux.h
===
--- clang/lib/Driver/ToolChains/Linux.h
+++ clang/lib/Driver/ToolChains/Linux.h
@@ -49,6 +49,11 @@
 
   std::vector ExtraOpts;
 
+  llvm::DenormalMode getDefaultDenormalModeForType(
+const llvm::opt::ArgList ,
+Action::OffloadKind DeviceOffloadKind,
+const llvm::fltSemantics *FPType = nullptr) const override;
+
 protected:
   Tool *buildAssembler() const override;
   Tool *buildLinker() const override;
Index: clang/lib/Driver/ToolChains/Linux.cpp
===
--- clang/lib/Driver/ToolChains/Linux.cpp
+++ clang/lib/Driver/ToolChains/Linux.cpp
@@ -1044,3 +1044,22 @@
 Twine("-u", llvm::getInstrProfRuntimeHookVarName(;
   ToolChain::addProfileRTLibs(Args, CmdArgs);
 }
+
+llvm::DenormalMode Linux::getDefaultDenormalModeForType(
+  const llvm::opt::ArgList ,
+  Action::OffloadKind DeviceOffloadKind,
+  const llvm::fltSemantics *FPType) const {
+  switch (getTriple().getArch()) {
+  case llvm::Triple::x86:
+  case llvm::Triple::x86_64: {
+std::string Unused;
+// DAZ and FTZ are turned on in crtfastmath.o
+if (!DriverArgs.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles) &&
+isFastMathRuntimeAvailable(DriverArgs, Unused))
+  return llvm::DenormalMode::getPreserveSign();
+return llvm::DenormalMode::getIEEE();
+  }
+  default:
+return llvm::DenormalMode::getIEEE();
+  }
+}
Index: clang/lib/Driver/ToolChains/Gnu.cpp
===
--- clang/lib/Driver/ToolChains/Gnu.cpp
+++ clang/lib/Driver/ToolChains/Gnu.cpp
@@ -502,7 +502,7 @@
 }
 
 // Add crtfastmath.o if available and fast math is enabled.
-ToolChain.AddFastMathRuntimeIfAvailable(Args, CmdArgs);
+

[PATCH] D69979: clang: Guess at some platform FTZ/DAZ default settings

[Sanjay Patel via Phabricator via cfe-commits]

spatel added a subscriber: andreadb.
spatel added inline comments.



Comment at: clang/include/clang/Driver/ToolChain.h:580
+  /// This checks for presence of the -Ofast, -ffast-math or -funsafe-math 
flags.
+  virtual bool FastMathRuntimeIsAvailable(
+const llvm::opt::ArgList , std::string ) const;

Formatting nit - prefer to start with verb and lower-case: 
isFastMathRuntimeAvailable() or hasFastMathRuntime().



Comment at: clang/include/clang/Driver/ToolChain.h:587
   /// This checks for presence of the -Ofast, -ffast-math or -funsafe-math 
flags.
-  virtual bool AddFastMathRuntimeIfAvailable(
-  const llvm::opt::ArgList , llvm::opt::ArgStringList ) const;
+  bool AddFastMathRuntimeIfAvailable(
+const llvm::opt::ArgList , llvm::opt::ArgStringList ) const;

Add -> add



Comment at: clang/lib/Driver/ToolChains/PS4CPU.h:95-96
+const llvm::fltSemantics *FPType) const override {
+// DAZ and FTZ are on by default.
+return llvm::DenormalMode::getPreserveSign();
+  }

@probinson / @andreadb - is this correct for PS4? or is there some equivalent 
to the Linux startup file?


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[PATCH] D69979: clang: Guess at some platform FTZ/DAZ default settings

[Matt Arsenault via Phabricator via cfe-commits]

arsenm updated this revision to Diff 231726.
arsenm added a comment.

DAZ/FTZ seem to be set in crtfastmath.o, so try to reproduce the logic for 
linking that


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Files:
  clang/include/clang/Driver/ToolChain.h
  clang/lib/Driver/ToolChain.cpp
  clang/lib/Driver/ToolChains/Linux.cpp
  clang/lib/Driver/ToolChains/Linux.h
  clang/lib/Driver/ToolChains/PS4CPU.h
  clang/test/Driver/default-denormal-fp-math.c

Index: clang/test/Driver/default-denormal-fp-math.c
===
--- /dev/null
+++ clang/test/Driver/default-denormal-fp-math.c
@@ -0,0 +1,19 @@
+// RUN: %clang -### -target arm-unknown-linux-gnu -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
+// RUN: %clang -### -target i386-unknown-linux-gnu -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
+
+// RUN: %clang -### -target x86_64-unknown-linux-gnu --sysroot=%S/Inputs/basic_linux_tree -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
+
+// crtfastmath enables ftz and daz
+// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffast-math --sysroot=%S/Inputs/basic_linux_tree -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-ZEROSIGN %s
+
+// crt not linked in with nostartfiles
+// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffast-math -nostartfiles --sysroot=%S/Inputs/basic_linux_tree -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
+
+// If there's no crtfastmath, don't assume ftz/daz
+// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffast-math --sysroot=/dev/null -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
+
+// RUN: %clang -### -target x86_64-scei-ps4 -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-ZEROSIGN %s
+
+
+// CHECK-IEEE: -fdenormal-fp-math=ieee,ieee
+// CHECK-ZEROSIGN: -fdenormal-fp-math=preserve-sign,preserve-sign
Index: clang/lib/Driver/ToolChains/PS4CPU.h
===
--- clang/lib/Driver/ToolChains/PS4CPU.h
+++ clang/lib/Driver/ToolChains/PS4CPU.h
@@ -88,6 +88,14 @@
   // capable of unit splitting.
   bool canSplitThinLTOUnit() const override { return false; }
 
+  llvm::DenormalMode getDefaultDenormalModeForType(
+const llvm::opt::ArgList ,
+Action::OffloadKind DeviceOffloadKind,
+const llvm::fltSemantics *FPType) const override {
+// DAZ and FTZ are on by default.
+return llvm::DenormalMode::getPreserveSign();
+  }
+
 protected:
   Tool *buildAssembler() const override;
   Tool *buildLinker() const override;
Index: clang/lib/Driver/ToolChains/Linux.h
===
--- clang/lib/Driver/ToolChains/Linux.h
+++ clang/lib/Driver/ToolChains/Linux.h
@@ -49,6 +49,11 @@
 
   std::vector ExtraOpts;
 
+  llvm::DenormalMode getDefaultDenormalModeForType(
+const llvm::opt::ArgList ,
+Action::OffloadKind DeviceOffloadKind,
+const llvm::fltSemantics *FPType = nullptr) const override;
+
 protected:
   Tool *buildAssembler() const override;
   Tool *buildLinker() const override;
Index: clang/lib/Driver/ToolChains/Linux.cpp
===
--- clang/lib/Driver/ToolChains/Linux.cpp
+++ clang/lib/Driver/ToolChains/Linux.cpp
@@ -1044,3 +1044,22 @@
 Twine("-u", llvm::getInstrProfRuntimeHookVarName(;
   ToolChain::addProfileRTLibs(Args, CmdArgs);
 }
+
+llvm::DenormalMode Linux::getDefaultDenormalModeForType(
+  const llvm::opt::ArgList ,
+  Action::OffloadKind DeviceOffloadKind,
+  const llvm::fltSemantics *FPType) const {
+  switch (getTriple().getArch()) {
+  case llvm::Triple::x86:
+  case llvm::Triple::x86_64: {
+std::string Unused;
+// DAZ and FTZ are turned on in crtfastmath.o
+if (!DriverArgs.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles) &&
+FastMathRuntimeIsAvailable(DriverArgs, Unused))
+  return llvm::DenormalMode::getPreserveSign();
+return llvm::DenormalMode::getIEEE();
+  }
+  default:
+return llvm::DenormalMode::getIEEE();
+  }
+}
Index: clang/lib/Driver/ToolChain.cpp
===
--- clang/lib/Driver/ToolChain.cpp
+++ clang/lib/Driver/ToolChain.cpp
@@ -915,28 +915,35 @@
   CmdArgs.push_back("-lcc_kext");
 }
 
-bool ToolChain::AddFastMathRuntimeIfAvailable(const ArgList ,
-  ArgStringList ) const {
+bool ToolChain::FastMathRuntimeIsAvailable(const ArgList ,
+   std::string ) const {
   // Do not check for -fno-fast-math or -fno-unsafe-math when -Ofast passed
   // (to keep the linker options consistent with gcc and clang itself).
   if (!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,
-  

[PATCH] D69979: clang: Guess at some platform FTZ/DAZ default settings

[Sanjay Patel via Phabricator via cfe-commits]

spatel added a comment.

In D69979#1749198 , @arsenm wrote:

> I just posted the test I wrote here: https://github.com/arsenm/subnormal_test


Thanks. I tried compiling with gcc (can't trust clang since it doesn't honor 
#pragma STDC FENV_ACCESS ON?). 
And running that on a Ubuntu 17.10 x86-64 system, it's behaving as I would 
expect. If you compile without -ffast-math,  it asserts:

  With denormals disabled
  a.out: subnormal_test.cpp:33: void fp32_denorm_test(): Assertion 
`std::fpclassify(subnormal) == FP_SUBNORMAL' failed.

And if you compile with -ffast-math, it asserts:

  In default FP mode
  a.out: subnormal_test.cpp:33: void fp32_denorm_test(): Assertion 
`std::fpclassify(subnormal) == FP_SUBNORMAL' failed.

This is what I see compiling Craig's csr tester:

  $ cc -O2 csr.c && ./a.out
  1f80
  $ cc -O2 csr.c -ffast-math && ./a.out
  9fc0

FZ is bit 15 (0x8000) and DAZ is bit 6 (0x0040), so they are clear in default 
(IEEE) mode and set with -ffast-math.


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[PATCH] D69979: clang: Guess at some platform FTZ/DAZ default settings

[Matt Arsenault via Phabricator via cfe-commits]

arsenm added a comment.

In D69979#1746043 , @spatel wrote:

> In D69979#1740294 , @arsenm wrote:
>
> > In D69979#1738099 , @craig.topper 
> > wrote:
> >
> > > I checked Redhat 7.4 that's on the server I'm using for work. And I had a 
> > > coworker check his Ubuntu 18.04 system with this program. And both 
> > > systems printed 1f80 as the value of MXCSR which shows FTZ and DAZ are 
> > > both 0. Are you seeing something different?
> > >
> > >   #include 
> > >   #include 
> > >  
> > >   int main() {
> > > int csr = _mm_getcsr();
> > > printf("%x\n", csr);
> > > return 0;
> > >   }
> > >
> >
> >
> > I see the value as 1f80. However the test program I wrote suggests the 
> > default is to flush (and what the comments in bug 34994 suggest?):
>
>
> Is the test program attached somewhere? 
>  Bug 34994 (https://bugs.llvm.org/show_bug.cgi?id=34994) was limited to 
> changing cases where we are running in some kind of loose-FP environment 
> (otherwise, we would not be generating a sqrt estimate sequence at all). In 
> the default (IEEE-compliant) environment, x86 would use a full-precision sqrt 
> instruction or make a call to libm sqrt.


I just posted the test I wrote here: https://github.com/arsenm/subnormal_test


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[PATCH] D69979: clang: Guess at some platform FTZ/DAZ default settings

[Sanjay Patel via Phabricator via cfe-commits]

spatel added a comment.

In D69979#1740294 , @arsenm wrote:

> In D69979#1738099 , @craig.topper 
> wrote:
>
> > I checked Redhat 7.4 that's on the server I'm using for work. And I had a 
> > coworker check his Ubuntu 18.04 system with this program. And both systems 
> > printed 1f80 as the value of MXCSR which shows FTZ and DAZ are both 0. Are 
> > you seeing something different?
> >
> >   #include 
> >   #include 
> >  
> >   int main() {
> > int csr = _mm_getcsr();
> > printf("%x\n", csr);
> > return 0;
> >   }
> >
>
>
> I see the value as 1f80. However the test program I wrote suggests the 
> default is to flush (and what the comments in bug 34994 suggest?):


Is the test program attached somewhere? 
Bug 34994 (https://bugs.llvm.org/show_bug.cgi?id=34994) was limited to changing 
cases where we are running in some kind of loose-FP environment (otherwise, we 
would not be generating a sqrt estimate sequence at all). In the default 
(IEEE-compliant) environment, x86 would use a full-precision sqrt instruction 
or make a call to libm sqrt.


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[PATCH] D69979: clang: Guess at some platform FTZ/DAZ default settings

[Matt Arsenault via Phabricator via cfe-commits]

arsenm added a comment.

In D69979#1738099 , @craig.topper 
wrote:

> I checked Redhat 7.4 that's on the server I'm using for work. And I had a 
> coworker check his Ubuntu 18.04 system with this program. And both systems 
> printed 1f80 as the value of MXCSR which shows FTZ and DAZ are both 0. Are 
> you seeing something different?
>
>   #include 
>   #include 
>  
>   int main() {
> int csr = _mm_getcsr();
> printf("%x\n", csr);
> return 0;
>   }
>


I see the value as 1f80. However the test program I wrote suggests the default 
is to flush (and what the comments in bug 34994 suggest?):

  In default FP mode
  neg_subnormal + neg_subnormal: -0x0p+0
  neg_subnormal + neg_zero: -0x0p+0
  sqrtf subnormal: 0x0p+0
  sqrtf neg_subnormal: -0x0p+0
  sqrtf neg_zero: -0x0p+0
  
  With denormals disabled
  neg_subnormal + neg_subnormal: -0x0p+0
  neg_subnormal + neg_zero: -0x0p+0
  sqrtf subnormal: 0x0p+0
  sqrtf neg_subnormal: -0x0p+0
  sqrtf neg_zero: -0x0p+0
  
  With denormals enabled
  neg_subnormal + neg_subnormal: -0x1p-126
  neg_subnormal + neg_zero: -0x1p-127
  sqrtf subnormal: 0x1.6a09e6p-64
  sqrtf neg_subnormal: -nan
  sqrtf neg_zero: -0x0p+0
  
  With daz only
  neg_subnormal + neg_subnormal: -0x0p+0
  neg_subnormal + neg_zero: -0x0p+0
  sqrtf subnormal: 0x0p+0
  sqrtf neg_subnormal: -0x0p+0
  sqrtf neg_zero: -0x0p+0
  
  With ftz only
  neg_subnormal + neg_subnormal: -0x1p-126
  neg_subnormal + neg_zero: -0x0p+0
  sqrtf subnormal: 0x1.6a09e6p-64
  sqrtf neg_subnormal: -nan
  sqrtf neg_zero: -0x0p+0


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[PATCH] D69979: clang: Guess at some platform FTZ/DAZ default settings

[Matt Arsenault via Phabricator via cfe-commits]

arsenm added a comment.

In D69979#1738723 , @spatel wrote:

> Also, I may have missed some discussions. Does this patch series replace the 
> proposal to add instruction-level FMF for denorms?
>  http://lists.llvm.org/pipermail/llvm-dev/2019-September/135183.html
>
> Ie, did we decide that a function-level attribute is good enough?


I think this is an orthogonal question. I would still find a ftz flag useful 
even in the presence of this attribute indicating flushing. For AMDGPU it would 
be useful with a specific instruction context to allow flushing even when the 
default mode is set to not flush. For example llvm.fmuladd could be emitted 
with an ftz flag which would select to an instruction that would ordinarily be 
illegal if denormals are enabled


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[PATCH] D69979: clang: Guess at some platform FTZ/DAZ default settings

[Sanjay Patel via Phabricator via cfe-commits]

spatel added a reviewer: cameron.mcinally.
spatel added a comment.

Also, I may have missed some discussions. Does this patch series replace the 
proposal to add instruction-level FMF for denorms?
http://lists.llvm.org/pipermail/llvm-dev/2019-September/135183.html

Ie, did we decide that a function-level attribute is good enough?


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[PATCH] D69979: clang: Guess at some platform FTZ/DAZ default settings

[Sanjay Patel via Phabricator via cfe-commits]

spatel added a comment.

In D69979#1738099 , @craig.topper 
wrote:

> I checked Redhat 7.4 that's on the server I'm using for work. And I had a 
> coworker check his Ubuntu 18.04 system with this program. And both systems 
> printed 1f80 as the value of MXCSR which shows FTZ and DAZ are both 0. Are 
> you seeing something different?


AFAIK, x86(-64) Linux is IEEE-compliant by default. It's only when compiling 
with -ffast-math that clang/gcc link in the startup routine to set FTZ/DAZ. So 
this patch should use that same mechanism to set the denorm mode. See: 
https://reviews.llvm.org/rL165240

@RKSimon - is it the same on PS4?


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[PATCH] D69979: clang: Guess at some platform FTZ/DAZ default settings

[Craig Topper via Phabricator via cfe-commits]

craig.topper added a comment.

I checked Redhat 7.4 that's on the server I'm using for work. And I had a 
coworker check his Ubuntu 18.04 system with this program. And both systems 
printed 1f80 as the value of MXCSR which shows FTZ and DAZ are both 0. Are you 
seeing something different?

  #include 
  #include 
  
  int main() {
int csr = _mm_getcsr();
printf("%x\n", csr);
return 0;
  }


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[PATCH] D69979: clang: Guess at some platform FTZ/DAZ default settings

[Matt Arsenault via Phabricator via cfe-commits]

arsenm created this revision.
arsenm added reviewers: spatel, craig.topper, RKSimon, hfinkel, probinson.
Herald added a subscriber: wdng.
arsenm added a parent revision: D69978: Separately track input and output 
denormal mode.

This is to avoid performance regressions when the default attribute
behavior is fixed to assume ieee.

  

I tested the default on x86_64 ubuntu, which seems to default to
FTZ/DAZ, but am guessing for x86 and PS4.


https://reviews.llvm.org/D69979

Files:
  clang/lib/Driver/ToolChains/Linux.cpp
  clang/lib/Driver/ToolChains/Linux.h
  clang/lib/Driver/ToolChains/PS4CPU.h
  clang/test/Driver/default-denormal-fp-math.c


Index: clang/test/Driver/default-denormal-fp-math.c
===
--- /dev/null
+++ clang/test/Driver/default-denormal-fp-math.c
@@ -0,0 +1,7 @@
+// RUN: %clang -### -target arm-unknown-linux-gnu -c %s -v 2>&1 | FileCheck 
-check-prefix=CHECK-IEEE %s
+// RUN: %clang -### -target i386-unknown-linux-gnu -c %s -v 2>&1 | FileCheck 
-check-prefix=CHECK-ZEROSIGN %s
+// RUN: %clang -### -target x86_64-unknown-linux-gnu -c %s -v 2>&1 | FileCheck 
-check-prefix=CHECK-ZEROSIGN %s
+// RUN: %clang -### -target x86_64-scei-ps4 -c %s -v 2>&1 | FileCheck 
-check-prefix=CHECK-ZEROSIGN %s
+
+// CHECK-IEEE: -fdenormal-fp-math=ieee,ieee
+// CHECK-ZEROSIGN: -fdenormal-fp-math=preserve-sign,preserve-sign
Index: clang/lib/Driver/ToolChains/PS4CPU.h
===
--- clang/lib/Driver/ToolChains/PS4CPU.h
+++ clang/lib/Driver/ToolChains/PS4CPU.h
@@ -88,6 +88,14 @@
   // capable of unit splitting.
   bool canSplitThinLTOUnit() const override { return false; }
 
+  llvm::DenormalMode getDefaultDenormalModeForType(
+const llvm::opt::ArgList ,
+Action::OffloadKind DeviceOffloadKind,
+const llvm::fltSemantics *FPType) const override {
+// DAZ and FTZ are on by default.
+return llvm::DenormalMode::getPreserveSign();
+  }
+
 protected:
   Tool *buildAssembler() const override;
   Tool *buildLinker() const override;
Index: clang/lib/Driver/ToolChains/Linux.h
===
--- clang/lib/Driver/ToolChains/Linux.h
+++ clang/lib/Driver/ToolChains/Linux.h
@@ -49,6 +49,11 @@
 
   std::vector ExtraOpts;
 
+  llvm::DenormalMode getDefaultDenormalModeForType(
+const llvm::opt::ArgList ,
+Action::OffloadKind DeviceOffloadKind,
+const llvm::fltSemantics *FPType = nullptr) const override;
+
 protected:
   Tool *buildAssembler() const override;
   Tool *buildLinker() const override;
Index: clang/lib/Driver/ToolChains/Linux.cpp
===
--- clang/lib/Driver/ToolChains/Linux.cpp
+++ clang/lib/Driver/ToolChains/Linux.cpp
@@ -1044,3 +1044,17 @@
 Twine("-u", llvm::getInstrProfRuntimeHookVarName(;
   ToolChain::addProfileRTLibs(Args, CmdArgs);
 }
+
+llvm::DenormalMode Linux::getDefaultDenormalModeForType(
+  const llvm::opt::ArgList ,
+  Action::OffloadKind DeviceOffloadKind,
+  const llvm::fltSemantics *FPType) const {
+  switch (getTriple().getArch()) {
+  case llvm::Triple::x86:
+  case llvm::Triple::x86_64:
+// DAZ and FTZ are on by default.
+return llvm::DenormalMode::getPreserveSign();
+  default:
+return llvm::DenormalMode::getIEEE();
+  }
+}


Index: clang/test/Driver/default-denormal-fp-math.c
===
--- /dev/null
+++ clang/test/Driver/default-denormal-fp-math.c
@@ -0,0 +1,7 @@
+// RUN: %clang -### -target arm-unknown-linux-gnu -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
+// RUN: %clang -### -target i386-unknown-linux-gnu -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-ZEROSIGN %s
+// RUN: %clang -### -target x86_64-unknown-linux-gnu -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-ZEROSIGN %s
+// RUN: %clang -### -target x86_64-scei-ps4 -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-ZEROSIGN %s
+
+// CHECK-IEEE: -fdenormal-fp-math=ieee,ieee
+// CHECK-ZEROSIGN: -fdenormal-fp-math=preserve-sign,preserve-sign
Index: clang/lib/Driver/ToolChains/PS4CPU.h
===
--- clang/lib/Driver/ToolChains/PS4CPU.h
+++ clang/lib/Driver/ToolChains/PS4CPU.h
@@ -88,6 +88,14 @@
   // capable of unit splitting.
   bool canSplitThinLTOUnit() const override { return false; }
 
+  llvm::DenormalMode getDefaultDenormalModeForType(
+const llvm::opt::ArgList ,
+Action::OffloadKind DeviceOffloadKind,
+const llvm::fltSemantics *FPType) const override {
+// DAZ and FTZ are on by default.
+return llvm::DenormalMode::getPreserveSign();
+  }
+
 protected:
   Tool *buildAssembler() const override;
   Tool *buildLinker() const override;
Index: clang/lib/Driver/ToolChains/Linux.h
===
--- clang/lib/Driver/ToolChains/Linux.h
+++ clang/lib/Driver/ToolChains/Linux.h
@@