Bundle operands to specify denormal modes

llvm/docs/LangRef.rst

@@ -3084,7 +3084,10 @@ floating-point control modes and the treatment of status bits respectively.
 
 An operand bundle tagged with "fp.control" contains information about the
 control modes used for the operation execution. Operands specified in this
-bundle represent particular options. Currently, only rounding mode is supported.
+bundle represent particular options. The following modes are supported:
+
+* rounding mode,
+* denormal behavior.
 
 Rounding mode is represented by a metadata string value, which specifies the
 the mode used for the operation evaluation. Possible values are:
@@ -3103,6 +3106,34 @@ rounding rounding mode is taken from the control register (dynamic rounding).
 In the particular case of :ref:`default floating-point environment <floatenv>`,
 the operation uses rounding to nearest, ties to even.
 
+Denormal behavior defines whether denormal values are flushed to zero during
+the call's execution. This behavior is specified separately for input and
+output values. Such specification is a string, which starts with
+"denorm.in=" or "denorm.out=" respectively. The remainder of the string should
+be one of the values:
+
+::
+
+    "ieee"  - preserve denormals,
+    "zero"  - flush to +0.0 or -0.0 depending on value sign,
+    "pzero" - flush to +0.0,
+    "dyn"   - concrete mode is read from some register.
+
+Such bundle operand specifies denormal behavior for all floating-point types.
+It is possible to override denormal behavior for specific type, if the target
+supports that. Now only type "f32" allows such overriding, if a bundle operand
+has prefix "denorm.f32.in=" or "denormal.f32.out=", its specifies denormal mode
+for ``float`` values in the affected instruction. For example:
+
+.. code-block:: llvm
+
+    ; denormal arguments are flushed to zero preserving sign.
+    call float @llvm.trunc.f32(float %x) [ "fp.control"(metadata !"denorm.in=ieee", metadata !"denorm.f32.in=zero") ]
+
+    ; denormal arguments are flushed to +0.0.
+    call float @llvm.trunc.f32(float %x) [ "fp.control"(metadata !"denorm.in=pzero") ]
+
+
 An operand bundle tagged with "fp.except" may be associated with operations
 that can read or write floating-point exception flags. It contains a single
 metadata string value, which can have one of the following values:

llvm/include/llvm/ADT/FloatingPointMode.h

@@ -234,6 +234,39 @@ void DenormalMode::print(raw_ostream &OS) const {
   OS << denormalModeKindName(Output) << ',' << denormalModeKindName(Input);
 }
 
+/// If the specified string represents denormal mode as used in operand bundles,
+/// returns the corresponding mode.
+inline std::optional<DenormalMode::DenormalModeKind>
+parseDenormalKindFromOperandBundle(StringRef Str) {
+  if (Str == "ieee")
+    return DenormalMode::IEEE;
+  if (Str == "zero")
+    return DenormalMode::PreserveSign;
+  if (Str == "pzero")
+    return DenormalMode::PositiveZero;
+  if (Str == "dyn")
+    return DenormalMode::Dynamic;
+  return std::nullopt;
+}
+
+/// Converts the specified denormal mode into string suitable for use in an
+/// operand bundle.
+inline std::optional<StringRef>
+printDenormalForOperandBundle(DenormalMode::DenormalModeKind Mode) {
+  switch (Mode) {
+  case DenormalMode::IEEE:
+    return "ieee";
+  case DenormalMode::PreserveSign:
+    return "zero";
+  case DenormalMode::PositiveZero:
+    return "pzero";
+  case DenormalMode::Dynamic:
+    return "dyn";
+  default:
+    return std::nullopt;
+  }
+}
+
 /// Floating-point class tests, supported by 'is_fpclass' intrinsic. Actual
 /// test may be an OR combination of basic tests.
 enum FPClassTest : unsigned {

llvm/include/llvm/IR/InstrTypes.h

@@ -1092,12 +1092,27 @@ template <typename InputTy> class OperandBundleDefT {
 using OperandBundleDef = OperandBundleDefT<Value *>;
 using ConstOperandBundleDef = OperandBundleDefT<const Value *>;
 
+std::optional<StringRef> getBundleOperandByPrefix(OperandBundleUse Bundle,
+                                                  StringRef Prefix);
+void addOperandToBundleTag(LLVMContext &Ctx,
+                           SmallVectorImpl<OperandBundleDef> &Bundles,
+                           StringRef Tag, size_t PrefixSize, StringRef Val);
+
 void addFPRoundingBundle(LLVMContext &Ctx,
                          SmallVectorImpl<OperandBundleDef> &Bundles,
                          RoundingMode Rounding);
 void addFPExceptionBundle(LLVMContext &Ctx,
                           SmallVectorImpl<OperandBundleDef> &Bundles,
                           fp::ExceptionBehavior Except);
+std::optional<DenormalMode::DenormalModeKind>
+getDenormModeBundle(const OperandBundleUse &Control, bool Unput,
+                    const fltSemantics *FPSem);
+void addInputDenormBundle(LLVMContext &Ctx,
+                          SmallVectorImpl<OperandBundleDef> &Bundles,
+                          DenormalMode::DenormalModeKind Mode);
+void addOutputDenormBundle(LLVMContext &Ctx,
+                           SmallVectorImpl<OperandBundleDef> &Bundles,
+                           DenormalMode::DenormalModeKind Mode);
 
 //===----------------------------------------------------------------------===//
 //                               CallBase Class
@@ -2171,6 +2186,22 @@ class CallBase : public Instruction {
   /// Return exception behavior specified for this call.
   fp::ExceptionBehavior getExceptionBehavior() const;
 
+  /// Return input denormal mode specified by operand bundles.
+  std::optional<DenormalMode::DenormalModeKind>
+  getInputDenormMode(const fltSemantics *FPSem = nullptr) const;
+
+  /// Return output denormal mode specified by operand bundles.
+  std::optional<DenormalMode::DenormalModeKind>
+  getOutputDenormMode(const fltSemantics *FPSem = nullptr) const;
+
+  /// Return input denormal mode specified by operand bundles.
+  std::optional<DenormalMode::DenormalModeKind>
+  getInputDenormModeFromBundle(const fltSemantics *FPSem = nullptr) const;
+
+  /// Return output denormal mode specified by operand bundles.
+  std::optional<DenormalMode::DenormalModeKind>
+  getOutputDenormModeFromBundle(const fltSemantics *FPSem = nullptr) const;
+
   /// Used to keep track of an operand bundle.  See the main comment on
   /// OperandBundleUser above.
   struct BundleOpInfo {

llvm/lib/Analysis/ConstantFolding.cpp

@@ -1354,6 +1354,11 @@ static ConstantFP *flushDenormalConstantFP(ConstantFP *CFP,
   if (!APF.isDenormal())
     return CFP;
 
+  if (auto *CB = dyn_cast_or_null<CallBase>(Inst)) {
+    auto Mode = IsOutput ? CB->getOutputDenormMode() : CB->getInputDenormMode();
+    return flushDenormalConstant(CFP->getType(), APF, *Mode);
+  }
+
   DenormalMode Mode = getInstrDenormalMode(Inst, CFP->getType());
   return flushDenormalConstant(CFP->getType(), APF,
                                IsOutput ? Mode.Output : Mode.Input);
@@ -2976,12 +2981,20 @@ static Constant *ConstantFoldIntrinsicCall2(Intrinsic::ID IntrinsicID, Type *Ty,
   }
 
   if (const auto *Op1 = dyn_cast<ConstantFP>(Operands[0])) {
-    const APFloat &Op1V = Op1->getValueAPF();
+    ConstantFP *Op1F =
+        flushDenormalConstantFP(const_cast<ConstantFP *>(Op1), Call, false);
+    if (!Op1F)
+      return nullptr;
+    const APFloat &Op1V = Op1F->getValueAPF();
 
     if (const auto *Op2 = dyn_cast<ConstantFP>(Operands[1])) {
       if (Op2->getType() != Op1->getType())
         return nullptr;
-      const APFloat &Op2V = Op2->getValueAPF();
+      ConstantFP *Op2F =
+          flushDenormalConstantFP(const_cast<ConstantFP *>(Op2), Call, false);
+      if (!Op2F)
+        return nullptr;
+      const APFloat &Op2V = Op2F->getValueAPF();
 
       if (const auto *ConstrIntr =
               dyn_cast_if_present<ConstrainedFPIntrinsic>(Call)) {
@@ -3011,8 +3024,10 @@ static Constant *ConstantFoldIntrinsicCall2(Intrinsic::ID IntrinsicID, Type *Ty,
           return evaluateCompare(Op1V, Op2V, ConstrIntr);
         }
         if (mayFoldConstrained(const_cast<ConstrainedFPIntrinsic *>(ConstrIntr),
-                               St))
-          return ConstantFP::get(Ty->getContext(), Res);
+                               St)) {
+          DenormalMode::DenormalModeKind Mode = *Call->getOutputDenormMode();
+          return flushDenormalConstant(Op2->getType(), Res, Mode);
+        }
         return nullptr;
       }