Recognize bit-manipulation idioms and emit bzhi/bts/btc/btr/bt on xarch

src/coreclr/jit/codegen.h

@@ -805,6 +805,7 @@ class CodeGen final : public CodeGenInterface
 
     void genCodeForDivMod(GenTreeOp* treeNode);
     void genCodeForMul(GenTreeOp* treeNode);
+    void genCodeForBitOp(GenTreeOp* treeNode);
     void genCodeForIncSaturate(GenTree* treeNode);
     void genCodeForMulHi(GenTreeOp* treeNode);
     void genLeaInstruction(GenTreeAddrMode* lea);

src/coreclr/jit/codegenxarch.cpp

@@ -1129,6 +1129,43 @@ void CodeGen::genCodeForBinary(GenTreeOp* treeNode)
     genProduceReg(treeNode);
 }
 
+//------------------------------------------------------------------------
+// genCodeForBitOp: Generate code for a GT_BIT_SET/GT_BIT_CLEAR/GT_BIT_INVERT operation, i.e. the
+// value-producing `bts`/`btr`/`btc` instructions which set, reset, or complement a single bit of op1
+// selected by op2.
+//
+// Arguments:
+//    treeNode - the node to generate the code for
+//
+void CodeGen::genCodeForBitOp(GenTreeOp* treeNode)
+{
+    assert(treeNode->OperIs(GT_BIT_SET, GT_BIT_CLEAR, GT_BIT_INVERT));
+
+    GenTree* op1 = treeNode->gtGetOp1(); // value (read-modify-write destination)
+    GenTree* op2 = treeNode->gtGetOp2(); // bit index
+
+    genConsumeOperands(treeNode);
+
+    regNumber targetReg  = treeNode->GetRegNum();
+    var_types targetType = genActualType(treeNode);
+    emitAttr  size       = emitTypeSize(targetType);
+    emitter*  emit       = GetEmitter();
+
+    assert((targetType == TYP_INT) || (targetType == TYP_LONG));
+    assert(op1->isUsedFromReg() && op2->isUsedFromReg());
+
+    instruction ins = treeNode->OperIs(GT_BIT_SET) ? INS_bts : treeNode->OperIs(GT_BIT_CLEAR) ? INS_btr : INS_btc;
+
+    // These are read-modify-write: the destination register also supplies the value operand.
+    inst_Mov(targetType, targetReg, op1->GetRegNum(), /* canSkip */ true);
+
+    // The BT-family reg,reg encoding places the destination in the r/m slot and the bit index in
+    // the reg slot, so the operands are passed reversed (see the note in instrsxarch.h).
+    emit->emitIns_R_R(ins, size, op2->GetRegNum(), targetReg);
+
+    genProduceReg(treeNode);
+}
+
 //------------------------------------------------------------------------
 // genCodeForMul: Generate code for a MUL operation.
 //
@@ -1892,6 +1929,12 @@ void CodeGen::genCodeForTreeNode(GenTree* treeNode)
             genCodeForBinary(treeNode->AsOp());
             break;
 
+        case GT_BIT_SET:
+        case GT_BIT_CLEAR:
+        case GT_BIT_INVERT:
+            genCodeForBitOp(treeNode->AsOp());
+            break;
+
         case GT_MUL:
             if (varTypeIsFloating(treeNode->TypeGet()))
             {

src/coreclr/jit/emitxarch.cpp

@@ -13495,6 +13495,15 @@ void emitter::emitDispIns(
                         break;
                 }
 
+                if ((ins == INS_bts) || (ins == INS_btr) || (ins == INS_btc))
+                {
+                    // The BT-family reg,reg encoding stores its operands reversed. Display them in
+                    // the normal `dest, index` order.
+                    printf("%s", emitRegName(id->idReg2(), tgtAttr));
+                    printf(", %s", emitRegName(id->idReg1(), srcAttr));
+                    break;
+                }
+
                 printf("%s", emitRegName(id->idReg1(), tgtAttr));
                 printf(", %s", emitRegName(id->idReg2(), srcAttr));
                 break;

src/coreclr/jit/gtlist.h

@@ -298,14 +298,16 @@ GTNODE(SH3ADD_UW        , GenTreeOp          ,0,0,GTK_BINOP|DBK_NOTHIR)
 GTNODE(ADD_UW           , GenTreeOp          ,0,0,GTK_BINOP|DBK_NOTHIR)
 // Maps to riscv64 slli.uw instruction. Computes result = zext(op1[31..0]) << imm.
 GTNODE(SLLI_UW          , GenTreeOp          ,0,0,GTK_BINOP|DBK_NOTHIR)
+#endif // TARGET_RISCV64
 
-// Maps to bset/bseti instruction. Computes result = op1 | (1 << op2)
+#if defined(TARGET_RISCV64) || defined(TARGET_XARCH)
+// Maps to riscv64 bset/bseti and xarch bts. Computes result = op1 | (1 << op2)
 GTNODE(BIT_SET          , GenTreeOp          ,0,0,GTK_BINOP|DBK_NOTHIR)
-// Maps to bclr/bclri instruction. Computes result = op1 & ~(1 << op2)
+// Maps to riscv64 bclr/bclri and xarch btr. Computes result = op1 & ~(1 << op2)
 GTNODE(BIT_CLEAR        , GenTreeOp          ,0,0,GTK_BINOP|DBK_NOTHIR)
-// Maps to binv/binvi instruction. Computes result = op1 ^ (1 << op2)
+// Maps to riscv64 binv/binvi and xarch btc. Computes result = op1 ^ (1 << op2)
 GTNODE(BIT_INVERT       , GenTreeOp          ,0,0,GTK_BINOP|DBK_NOTHIR)
-#endif
+#endif // TARGET_RISCV64 || TARGET_XARCH
 
 //-----------------------------------------------------------------------------
 //  Other nodes that look like unary/binary operators:

src/coreclr/jit/instrsxarch.h

@@ -95,6 +95,12 @@ INST4(lea,              "lea",              IUM_WR, BAD_CODE,     BAD_CODE,
 // and the registers need to be reversed to get the correct encoding.
 INST3(bt,               "bt",               IUM_RD, 0x0F00A3,     BAD_CODE,     0x0F00A3,                                1C,                2X,         INS_TT_NONE,    Undefined_OF   | Undefined_SF  | Undefined_ZF  | Undefined_AF  | Undefined_PF  | Writes_CF | Encoding_REX2)
 
+// BTS/BTR/BTC are only emitted in their reg,reg form (like BT the registers are reversed to get
+// the correct encoding). They read+write the first operand and write the old bit value to CF.
+INST3(bts,              "bts",              IUM_RW, 0x0F00AB,     BAD_CODE,     0x0F00AB,                                1C,                2X,         INS_TT_NONE,    Undefined_OF   | Undefined_SF  | Undefined_ZF  | Undefined_AF  | Undefined_PF  | Writes_CF | Encoding_REX2)
+INST3(btr,              "btr",              IUM_RW, 0x0F00B3,     BAD_CODE,     0x0F00B3,                                1C,                2X,         INS_TT_NONE,    Undefined_OF   | Undefined_SF  | Undefined_ZF  | Undefined_AF  | Undefined_PF  | Writes_CF | Encoding_REX2)
+INST3(btc,              "btc",              IUM_RW, 0x0F00BB,     BAD_CODE,     0x0F00BB,                                1C,                2X,         INS_TT_NONE,    Undefined_OF   | Undefined_SF  | Undefined_ZF  | Undefined_AF  | Undefined_PF  | Writes_CF | Encoding_REX2)
+
 INST3(bsr,              "bsr",              IUM_WR, BAD_CODE,     BAD_CODE,     0x0F00BD,                                3C,                1C,         INS_TT_NONE,    Undefined_OF   | Undefined_SF  | Writes_ZF     | Undefined_AF  | Undefined_PF  | Undefined_CF | Encoding_REX2)
 INST3(bsf,              "bsf",              IUM_WR, BAD_CODE,     BAD_CODE,     0x0F00BC,                                3C,                1C,         INS_TT_NONE,    Undefined_OF   | Undefined_SF  | Writes_ZF     | Undefined_AF  | Undefined_PF  | Undefined_CF | Encoding_REX2)
 

src/coreclr/jit/lower.cpp

@@ -4235,6 +4235,34 @@ GenTree* Lowering::OptimizeConstCompare(GenTree* cmp)
             test->gtOp2 = bitOp->gtGetOp2();
             return true;
         }
+
+#ifdef TARGET_XARCH
+        // Also recognize the arithmetic form `(x >> y) & 1`, i.e. AND(RSH|RSZ(x, y), 1), which
+        // tests bit `y` of `x` just like `x & (1 << y)`. Only bit 0 of the shifted value is kept so
+        // the shift kind is irrelevant, and `bt` masks the bit index modulo the operand size, which
+        // matches the C# masked-shift semantics even for an out-of-range `y`. Restricted to a
+        // variable index because a constant index keeps the shift, and `bt` has no immediate form
+        // here (a constant mask `test` is already optimal).
+        GenTree* shiftOp = test->gtOp1;
+        GenTree* oneOp   = test->gtOp2;
+        if (!oneOp->IsIntegralConst(1))
+            std::swap(shiftOp, oneOp);
+
+        if (oneOp->IsIntegralConst(1) && shiftOp->OperIs(GT_RSH, GT_RSZ) && varTypeIsIntOrI(shiftOp) &&
+            !shiftOp->gtGetOp2()->IsIntegralConst())
+        {
+            BlockRange().Remove(oneOp);
+            BlockRange().Remove(shiftOp);
+            test->gtOp1 = shiftOp->gtGetOp1();
+            test->gtOp2 = shiftOp->gtGetOp2();
+
+            // ContainCheckCompare is skipped when this transform succeeds, so clear any containment
+            // the value operand picked up from the removed shift (e.g. a `shrx` memory source) --
+            // the reg,reg `bt` form requires it in a register.
+            test->gtOp1->ClearContained();
+            return true;
+        }
+#endif // TARGET_XARCH
         return false;
     };
 

src/coreclr/jit/lower.h

@@ -509,7 +509,9 @@ class Lowering final : public Phase
     GenTree* TryLowerAndOpToResetLowestSetBit(GenTreeOp* andNode);
     GenTree* TryLowerAndOpToExtractLowestSetBit(GenTreeOp* andNode);
     GenTree* TryLowerAndOpToAndNot(GenTreeOp* andNode);
+    GenTree* TryLowerAndOpToZeroHighBits(GenTreeOp* andNode);
     GenTree* TryLowerXorOpToGetMaskUpToLowestSetBit(GenTreeOp* xorNode);
+    GenTree* TryLowerBitwiseOpToBitOp(GenTreeOp* binOp);
     void     LowerBswapOp(GenTreeOp* node);
     GenTree* LowerHWIntrinsicDotInnerMulSum(GenTreeHWIntrinsic* node);
 #elif defined(TARGET_ARM64)