[InstCombine] Fold fneg/fabs patterns with ppc_f128 (#130557)

dtcxzyw · web-flow · commit e710a5a9f274 · 2025-04-14T14:30:00.000+08:00
This patch is needed by llvm/llvm-project#130496.
diff --git a/llvm/include/llvm/ADT/APFloat.h b/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.
diff --git a/llvm/lib/Support/APFloat.cpp b/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.
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2645,7 +2645,8 @@ Instruction *InstCombinerImpl::visitAnd(BinaryOperator &I) {
       !Builder.GetInsertBlock()->getParent()->hasFnAttribute(
           Attribute::NoImplicitFloat)) {
     Type *EltTy = CastOp->getType()->getScalarType();
-    if (EltTy->isFloatingPointTy() && EltTy->isIEEE()) {
+    if (EltTy->isFloatingPointTy() &&
+        APFloat::hasSignBitInMSB(EltTy->getFltSemantics())) {
       Value *FAbs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, CastOp);
       return new BitCastInst(FAbs, I.getType());
     }
@@ -4058,7 +4059,8 @@ Instruction *InstCombinerImpl::visitOr(BinaryOperator &I) {
       !Builder.GetInsertBlock()->getParent()->hasFnAttribute(
           Attribute::NoImplicitFloat)) {
     Type *EltTy = CastOp->getType()->getScalarType();
-    if (EltTy->isFloatingPointTy() && EltTy->isIEEE()) {
+    if (EltTy->isFloatingPointTy() &&
+        APFloat::hasSignBitInMSB(EltTy->getFltSemantics())) {
       Value *FAbs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, CastOp);
       Value *FNegFAbs = Builder.CreateFNeg(FAbs);
       return new BitCastInst(FNegFAbs, I.getType());
@@ -4860,7 +4862,8 @@ Instruction *InstCombinerImpl::visitXor(BinaryOperator &I) {
         !Builder.GetInsertBlock()->getParent()->hasFnAttribute(
             Attribute::NoImplicitFloat)) {
       Type *EltTy = CastOp->getType()->getScalarType();
-      if (EltTy->isFloatingPointTy() && EltTy->isIEEE()) {
+      if (EltTy->isFloatingPointTy() &&
+          APFloat::hasSignBitInMSB(EltTy->getFltSemantics())) {
         Value *FNeg = Builder.CreateFNeg(CastOp);
         return new BitCastInst(FNeg, I.getType());
       }
diff --git a/llvm/test/Transforms/InstCombine/fabs-as-int.ll b/llvm/test/Transforms/InstCombine/fabs-as-int.ll
@@ -289,8 +289,8 @@ define i128 @fabs_as_int_ppc_fp128_f64_mask(ppc_fp128 %x) {
 define i128 @fabs_as_int_ppc_fp128_f128_mask(ppc_fp128 %x) {
 ; CHECK-LABEL: define i128 @fabs_as_int_ppc_fp128_f128_mask
 ; CHECK-SAME: (ppc_fp128 [[X:%.*]]) {
-; CHECK-NEXT:    [[BC:%.*]] = bitcast ppc_fp128 [[X]] to i128
-; CHECK-NEXT:    [[AND:%.*]] = and i128 [[BC]], 170141183460469231731687303715884105727
+; CHECK-NEXT:    [[TMP1:%.*]] = call ppc_fp128 @llvm.fabs.ppcf128(ppc_fp128 [[X]])
+; CHECK-NEXT:    [[AND:%.*]] = bitcast ppc_fp128 [[TMP1]] to i128
 ; CHECK-NEXT:    ret i128 [[AND]]
 ;
   %bc = bitcast ppc_fp128 %x to i128
diff --git a/llvm/test/Transforms/InstCombine/fneg-as-int.ll b/llvm/test/Transforms/InstCombine/fneg-as-int.ll
@@ -291,8 +291,8 @@ define i128 @fneg_as_int_ppc_fp128_f64_mask(ppc_fp128 %x) {
 define i128 @fneg_as_int_ppc_fp128_f128_mask(ppc_fp128 %x) {
 ; CHECK-LABEL: define i128 @fneg_as_int_ppc_fp128_f128_mask
 ; CHECK-SAME: (ppc_fp128 [[X:%.*]]) {
-; CHECK-NEXT:    [[BC:%.*]] = bitcast ppc_fp128 [[X]] to i128
-; CHECK-NEXT:    [[XOR:%.*]] = xor i128 [[BC]], -170141183460469231731687303715884105728
+; CHECK-NEXT:    [[TMP1:%.*]] = fneg ppc_fp128 [[X]]
+; CHECK-NEXT:    [[XOR:%.*]] = bitcast ppc_fp128 [[TMP1]] to i128
 ; CHECK-NEXT:    ret i128 [[XOR]]
 ;
   %bc = bitcast ppc_fp128 %x to i128
diff --git a/llvm/test/Transforms/InstCombine/fneg-fabs-as-int.ll b/llvm/test/Transforms/InstCombine/fneg-fabs-as-int.ll
@@ -317,8 +317,9 @@ define i128 @fneg_fabs_as_int_ppc_fp128_f64_mask(ppc_fp128 %x) {
 define i128 @fneg_fabs_as_int_ppc_fp128_f128_mask(ppc_fp128 %x) {
 ; CHECK-LABEL: define i128 @fneg_fabs_as_int_ppc_fp128_f128_mask
 ; CHECK-SAME: (ppc_fp128 [[X:%.*]]) {
-; CHECK-NEXT:    [[BC:%.*]] = bitcast ppc_fp128 [[X]] to i128
-; CHECK-NEXT:    [[OR:%.*]] = or i128 [[BC]], -170141183460469231731687303715884105728
+; CHECK-NEXT:    [[TMP1:%.*]] = call ppc_fp128 @llvm.fabs.ppcf128(ppc_fp128 [[X]])
+; CHECK-NEXT:    [[TMP2:%.*]] = fneg ppc_fp128 [[TMP1]]
+; CHECK-NEXT:    [[OR:%.*]] = bitcast ppc_fp128 [[TMP2]] to i128
 ; CHECK-NEXT:    ret i128 [[OR]]
 ;
   %bc = bitcast ppc_fp128 %x to i128
diff --git a/llvm/unittests/ADT/APFloatTest.cpp b/llvm/unittests/ADT/APFloatTest.cpp
@@ -8347,4 +8347,13 @@ 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_TRUE(APFloat::hasSignBitInMSB(APFloat::x87DoubleExtended()));
+  EXPECT_TRUE(APFloat::hasSignBitInMSB(APFloat::PPCDoubleDouble()));
+  EXPECT_TRUE(APFloat::hasSignBitInMSB(APFloat::IEEEquad()));
+  EXPECT_FALSE(APFloat::hasSignBitInMSB(APFloat::Float8E8M0FNU()));
+}
+
 } // namespace
