[ADT] Add hasSignBitInMSB helper

Author: dtcxzyw

llvm/include/llvm/ADT/APFloat.h

@@ -354,6 +354,7 @@ struct APFloatBase {
   static bool semanticsHasInf(const fltSemantics &);
   static bool semanticsHasNaN(const fltSemantics &);
   static bool isIEEELikeFP(const fltSemantics &);
+  static bool hasSignBitInMSB(const fltSemantics &);
 
   // Returns true if any number described by \p Src can be precisely represented
   // by a normal (not subnormal) value in \p Dst.

llvm/lib/Support/APFloat.cpp

@@ -125,6 +125,9 @@ struct fltSemantics {
 
   /* Whether this semantics can represent signed values */
   bool hasSignedRepr = true;
+
+  /* Whether the sign bit of this semantics is the most significant bit */
+  bool hasSignBitInMSB = true;
 };
 
 static constexpr fltSemantics semIEEEhalf = {15, -14, 11, 16};
@@ -144,9 +147,15 @@ static constexpr fltSemantics semFloat8E4M3B11FNUZ = {
     4, -10, 4, 8, fltNonfiniteBehavior::NanOnly, fltNanEncoding::NegativeZero};
 static constexpr fltSemantics semFloat8E3M4 = {3, -2, 5, 8};
 static constexpr fltSemantics semFloatTF32 = {127, -126, 11, 19};
-static constexpr fltSemantics semFloat8E8M0FNU = {
-    127,   -127, 1, 8, fltNonfiniteBehavior::NanOnly, fltNanEncoding::AllOnes,
-    false, false};
+static constexpr fltSemantics semFloat8E8M0FNU = {127,
+                                                  -127,
+                                                  1,
+                                                  8,
+                                                  fltNonfiniteBehavior::NanOnly,
+                                                  fltNanEncoding::AllOnes,
+                                                  false,
+                                                  false,
+                                                  false};
 
 static constexpr fltSemantics semFloat6E3M2FN = {
     4, -2, 3, 6, fltNonfiniteBehavior::FiniteOnly};
@@ -358,6 +367,10 @@ bool APFloatBase::isIEEELikeFP(const fltSemantics &semantics) {
   return SemanticsToEnum(semantics) <= S_IEEEquad;
 }
 
+bool APFloatBase::hasSignBitInMSB(const fltSemantics &semantics) {
+  return semantics.hasSignBitInMSB;
+}
+
 bool APFloatBase::isRepresentableAsNormalIn(const fltSemantics &Src,
                                             const fltSemantics &Dst) {
   // Exponent range must be larger.

llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

@@ -2641,7 +2641,10 @@ Instruction *InstCombinerImpl::visitAnd(BinaryOperator &I) {
   // TODO: Unify with APInt matcher. This version allows undef unlike m_APInt
   Value *CastOp;
   if (match(Op0, m_ElementWiseBitCast(m_Value(CastOp))) &&
-      CastOp->getType()->isFPOrFPVectorTy() && match(Op1, m_MaxSignedValue()) &&
+      CastOp->getType()->isFPOrFPVectorTy() &&
+      APFloat::hasSignBitInMSB(
+          CastOp->getType()->getScalarType()->getFltSemantics()) &&
+      match(Op1, m_MaxSignedValue()) &&
       !Builder.GetInsertBlock()->getParent()->hasFnAttribute(
           Attribute::NoImplicitFloat)) {
     Value *FAbs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, CastOp);
@@ -4050,7 +4053,10 @@ Instruction *InstCombinerImpl::visitOr(BinaryOperator &I) {
   // floating-point operation.
   Value *CastOp;
   if (match(Op0, m_ElementWiseBitCast(m_Value(CastOp))) &&
-      CastOp->getType()->isFPOrFPVectorTy() && match(Op1, m_SignMask()) &&
+      CastOp->getType()->isFPOrFPVectorTy() &&
+      APFloat::hasSignBitInMSB(
+          CastOp->getType()->getScalarType()->getFltSemantics()) &&
+      match(Op1, m_SignMask()) &&
       !Builder.GetInsertBlock()->getParent()->hasFnAttribute(
           Attribute::NoImplicitFloat)) {
     Value *FAbs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, CastOp);
@@ -4849,7 +4855,10 @@ Instruction *InstCombinerImpl::visitXor(BinaryOperator &I) {
     // TODO: Unify with APInt matcher. This version allows undef unlike m_APInt
     Value *CastOp;
     if (match(Op0, m_ElementWiseBitCast(m_Value(CastOp))) &&
-        CastOp->getType()->isFPOrFPVectorTy() && match(Op1, m_SignMask()) &&
+        CastOp->getType()->isFPOrFPVectorTy() &&
+        APFloat::hasSignBitInMSB(
+            CastOp->getType()->getScalarType()->getFltSemantics()) &&
+        match(Op1, m_SignMask()) &&
         !Builder.GetInsertBlock()->getParent()->hasFnAttribute(
             Attribute::NoImplicitFloat)) {
       Value *FNeg = Builder.CreateFNeg(CastOp);

llvm/unittests/ADT/APFloatTest.cpp

@@ -8347,4 +8347,10 @@ TEST(APFloatTest, AddOrSubtractSignificand) {
   Helper::runTest(true, false, 3, 0x10001, false, 7, 0x100, false, 6, 0x1e00,
                   lfLessThanHalf);
 }
+
+TEST(APFloatTest, hasSignBitInMSB) {
+  EXPECT_TRUE(APFloat::hasSignBitInMSB(APFloat::IEEEsingle()));
+  EXPECT_FALSE(APFloat::hasSignBitInMSB(APFloat::Float8E8M0FNU()));
+}
+
 } // namespace