[llvm-mca][AArch64] Add AArch64 version of clearsSuperRegisters.

llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCTargetDesc.cpp

@@ -432,6 +432,55 @@ class AArch64MCInstrAnalysis : public MCInstrAnalysis {
     return false;
   }
 
+  bool clearsSuperRegisters(const MCRegisterInfo &MRI, const MCInst &Inst,
+                            APInt &Mask) const override {
+    const MCInstrDesc &Desc = Info->get(Inst.getOpcode());
+    unsigned NumDefs = Desc.getNumDefs();
+    unsigned NumImplicitDefs = Desc.implicit_defs().size();
+    assert(Mask.getBitWidth() == NumDefs + NumImplicitDefs &&
+           "Unexpected number of bits in the mask!");
+    // 32-bit General Purpose Register class.
+    const MCRegisterClass &GPR32RC = MRI.getRegClass(AArch64::GPR32RegClassID);
+    // Floating Point Register classes.
+    const MCRegisterClass &FPR8RC = MRI.getRegClass(AArch64::FPR8RegClassID);
+    const MCRegisterClass &FPR16RC = MRI.getRegClass(AArch64::FPR16RegClassID);
+    const MCRegisterClass &FPR32RC = MRI.getRegClass(AArch64::FPR32RegClassID);
+    const MCRegisterClass &FPR64RC = MRI.getRegClass(AArch64::FPR64RegClassID);
+    const MCRegisterClass &FPR128RC =
+        MRI.getRegClass(AArch64::FPR128RegClassID);
+
+    auto ClearsSuperReg = [=](unsigned RegID) {
+      // An update to the lower 32 bits of a 64 bit integer register is
+      // architecturally defined to zero extend the upper 32 bits on a write.
+      if (GPR32RC.contains(RegID))
+        return true;
+      // SIMD&FP instructions operating on scalar data only acccess the lower
+      // bits of a register, the upper bits are zero extended on a write. For
+      // SIMD vector registers smaller than 128-bits, the upper 64-bits of the
+      // register are zero extended on a write.
+      // When VL is higher than 128 bits, any write to a SIMD&FP register sets
+      // bits higher than 128 to zero.
+      return FPR8RC.contains(RegID) || FPR16RC.contains(RegID) ||
+             FPR32RC.contains(RegID) || FPR64RC.contains(RegID) ||
+             FPR128RC.contains(RegID);
+    };
+
+    Mask.clearAllBits();
+    for (unsigned I = 0, E = NumDefs; I < E; ++I) {
+      const MCOperand &Op = Inst.getOperand(I);
+      if (ClearsSuperReg(Op.getReg()))
+        Mask.setBit(I);
+    }
+
+    for (unsigned I = 0, E = NumImplicitDefs; I < E; ++I) {
+      const MCPhysReg Reg = Desc.implicit_defs()[I];
+      if (ClearsSuperReg(Reg))
+        Mask.setBit(NumDefs + I);
+    }
+
+    return Mask.getBoolValue();
+  }
+
   std::vector<std::pair<uint64_t, uint64_t>>
   findPltEntries(uint64_t PltSectionVA, ArrayRef<uint8_t> PltContents,
                  const Triple &TargetTriple) const override {