[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 &DriverArgs,
+    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<std::string> ExtraOpts;
 
+  llvm::DenormalMode getDefaultDenormalModeForType(
+    const llvm::opt::ArgList &DriverArgs,
+    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 &DriverArgs,
+  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();
+  }
+}


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