[llvm] [RISCV][GISel] Add ISel supports for SHXADD from Zba extension (PR #67863)

[Craig Topper via llvm-commits]

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@@ -105,6 +112,110 @@ RISCVInstructionSelector::selectShiftMask(MachineOperand &Root) const {
   return {{[=](MachineInstrBuilder &MIB) { MIB.add(Root); }}};
 }
 
+InstructionSelector::ComplexRendererFns
+RISCVInstructionSelector::selectSHXADDOp(MachineOperand &Root,
+                                         unsigned ShAmt) const {
+  using namespace llvm::MIPatternMatch;
+  MachineFunction &MF = *Root.getParent()->getParent()->getParent();
+  MachineRegisterInfo &MRI = MF.getRegInfo();
+
+  if (!Root.isReg())
+    return std::nullopt;
+  Register RootReg = Root.getReg();
+
+  const unsigned XLen = STI.getXLen();
+  APInt Mask, C2;
+  Register RegY;
+  std::optional<bool> LeftShift;
+  // (and (shl y, c2), mask)
+  if (mi_match(RootReg, MRI,
+               m_GAnd(m_GShl(m_Reg(RegY), m_ICst(C2)), m_ICst(Mask))))
+    LeftShift = true;
+  // (and (lshr y, c2), mask)
+  else if (mi_match(RootReg, MRI,
+                    m_GAnd(m_GLShr(m_Reg(RegY), m_ICst(C2)), m_ICst(Mask))))
+    LeftShift = false;
+
+  if (LeftShift.has_value()) {
+    if (*LeftShift)
+      Mask &= maskTrailingZeros<uint64_t>(C2.getLimitedValue());
+    else
+      Mask &= maskTrailingOnes<uint64_t>(XLen - C2.getLimitedValue());
+
+    if (Mask.isShiftedMask()) {
+      unsigned Leading = XLen - Mask.getActiveBits();
+      unsigned Trailing = Mask.countr_zero();
+      // Given (and (shl y, c2), mask) in which mask has no leading zeros and
+      // c3 trailing zeros. We can use an SRLI by c3 - c2 followed by a SHXADD.
+      if (*LeftShift && Leading == 0 && C2.ult(Trailing) && Trailing == ShAmt) {
+        Register DstReg =
+            MRI.createGenericVirtualRegister(MRI.getType(RootReg));
+        return {{[=](MachineInstrBuilder &MIB) {
+          MachineIRBuilder(*MIB.getInstr())
+              .buildInstr(RISCV::SRLI, {DstReg}, {RegY})
+              .addImm(Trailing - C2.getLimitedValue());
+          MIB.addReg(DstReg);
+        }}};
+      }
+
+      // Given (and (lshr y, c2), mask) in which mask has c2 leading zeros and c3
+      // trailing zeros. We can use an SRLI by c2 + c3 followed by a SHXADD.
+      if (!*LeftShift && Leading == C2 && Trailing == ShAmt) {
+        Register DstReg =
+            MRI.createGenericVirtualRegister(MRI.getType(RootReg));
+        return {{[=](MachineInstrBuilder &MIB) {
+          MachineIRBuilder(*MIB.getInstr())
+              .buildInstr(RISCV::SRLI, {DstReg}, {RegY})
+              .addImm(Leading + Trailing);
+          MIB.addReg(DstReg);
+        }}};
+      }
+    }
+  }
+
+  LeftShift.reset();
+
+  // (shl (and y, mask), c2)
+  if (mi_match(RootReg, MRI,
+               m_GShl(m_OneNonDBGUse(m_GAnd(m_Reg(RegY), m_ICst(Mask))),
+                      m_ICst(C2))))
+    LeftShift = true;
+  // (lshr (and y, mask), c2)
+  else if (mi_match(RootReg, MRI,
+                    m_GLShr(m_OneNonDBGUse(m_GAnd(m_Reg(RegY), m_ICst(Mask))),
+                            m_ICst(C2))))
+    LeftShift = false;
+
+  if (LeftShift.has_value())
+    if (Mask.isShiftedMask()) {
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topperc wrote:

Can we merge this condition with the previous if?

https://github.com/llvm/llvm-project/pull/67863