[llvm] [llvm-mca][AArch64] Add AArch64 version of clearsSuperRegisters. (PR #92548)

[Rin Dobrescu via llvm-commits]

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@@ -432,6 +432,52 @@ 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 lower than 128-bit.
+    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);
+
+    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.
+      if (FPR8RC.contains(RegID) || FPR16RC.contains(RegID) ||
+          FPR32RC.contains(RegID) || FPR64RC.contains(RegID))
+        return true;
+      return false;
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Rin18 wrote:

Done

https://github.com/llvm/llvm-project/pull/92548