[clang] [llvm] Add support for flag output operand "=@cc" for SystemZ. (PR #125970)

[Ulrich Weigand via llvm-commits]

================
@@ -8030,7 +8077,431 @@ SDValue SystemZTargetLowering::combineBSWAP(
   return SDValue();
 }
 
+// Combine IPM sequence for flag output operands.
+static bool combineSRL_IPM_CCMask(SDValue &CCReg, int &CCValid, int &CCMask) {
+  // Convert CCVal to CCMask and update it along with  CCValid.
+  const auto convertCCValToCCMask = [&CCMask, &CCValid](int CCVal) {
+    bool Invert = false;
+    if (CCMask == SystemZ::CCMASK_CMP_NE)
+      Invert = !Invert;
+    if (CCMask == SystemZ::CCMASK_CMP_EQ || CCMask == SystemZ::CCMASK_CMP_NE) {
+      CCMask = CCMaskForSystemZCCVal(CCVal);
+      if (Invert)
+        CCMask ^= SystemZ::CCMASK_ANY;
+      CCValid = SystemZ::CCMASK_ANY;
+      return true;
+    } else if (CCMask == SystemZ::CCMASK_CMP_LT) {
+      // CC in range [0, CCVal).
+      CCMask = ((~0U << (4 - CCVal)) & SystemZ::CCMASK_ANY);
+      CCValid = SystemZ::CCMASK_ANY;
+      return true;
+    } else if (CCMask == SystemZ::CCMASK_CMP_GT) {
+      // CC in range (CCVal, 3].
+      CCMask = (~(~0U << (3 - CCVal))) & SystemZ::CCMASK_ANY;
+      CCValid = SystemZ::CCMASK_ANY;
+      return true;
+    }
+    return false;
+  };
+  // Check (SRL (IPM (CC))) and update CCReg to combine.
+  const auto isSRL_IPM_CCSequence = [&CCReg](SDNode *N) {
+    if (!N || N->getOpcode() != ISD::SRL)
+      return false;
+    auto *SRLCount = dyn_cast<ConstantSDNode>(N->getOperand(1));
+    if (!SRLCount || SRLCount->getZExtValue() != SystemZ::IPM_CC)
+      return false;
+    auto *IPM = N->getOperand(0).getNode();
+    if (!IPM || IPM->getOpcode() != SystemZISD::IPM)
+      return false;
+    auto *IPMOp0 = IPM->getOperand(0).getNode();
+    if (!IPMOp0 || IPMOp0->getNumOperands() < 2)
+      return false;
+    auto *RN = dyn_cast<RegisterSDNode>(IPMOp0->getOperand(1));
+    // Check if operand 1 is SystemZ::CC. Also, it avoids srl/ipm/tbegin and
+    // srl/ipm/tend kind of sequences.
+    if (!RN || !RN->getReg().isPhysical() || RN->getReg() != SystemZ::CC)
+      return false;
+    // Return the updated CCReg link.
+    CCReg = IPM->getOperand(0);
+    return true;
+  };
+  // Check if N has SystemZ::CC operand.
+  const auto isCCOperand = [](SDNode *N) {
+    if (!N || N->getNumOperands() < 2)
+      return false;
+    auto *RN = dyn_cast<RegisterSDNode>(N->getOperand(1));
+    if (!RN || !RN->getReg().isPhysical() || RN->getReg() != SystemZ::CC)
+      return false;
+    return true;
+  };
+
+  auto *CCNode = CCReg.getNode();
+  if (!CCNode)
+    return false;
+
+  int RestoreCCValid = CCValid;
+  // Optimize (TM (IPM (CC)))
+  if (CCNode->getOpcode() == SystemZISD::TM) {
+    bool Invert = false;
+    if (CCMask == SystemZ::CCMASK_TM_SOME_1)
+      Invert = !Invert;
+    auto *N = CCNode->getOperand(0).getNode();
+    auto Shift = dyn_cast<ConstantSDNode>(CCNode->getOperand(1));
+    if (!N || !Shift)
+      return false;
+    if (N->getOpcode() == SystemZISD::IPM) {
+      auto ShiftVal = Shift->getZExtValue();
+      if (ShiftVal == (1 << SystemZ::IPM_CC))
+        CCMask = SystemZ::CCMASK_CMP_GE;
+      if (Invert)
+        CCMask ^= CCValid;
+      // Return the updated CCReg link.
+      CCReg = N->getOperand(0);
+      return true;
+    } else if (N->getOpcode() == ISD::XOR) {
+      // Optimize (TM (XOR (OP1 OP2))).
+      auto *XOROp1 = N->getOperand(0).getNode();
+      auto *XOROp2 = N->getOperand(1).getNode();
+      if (!XOROp1 || !XOROp2)
+        return false;
+      // OP1. (SELECT_CCMASK (ICMP (SRL (IPM (CC))))).
+      // OP2. (SRL (IPM (CC))).
+      if (XOROp1->getOpcode() == SystemZISD::SELECT_CCMASK &&
+          isSRL_IPM_CCSequence(XOROp2)) {
+        auto *CCValid1 = dyn_cast<ConstantSDNode>(XOROp1->getOperand(2));
+        auto *CCMask1 = dyn_cast<ConstantSDNode>(XOROp1->getOperand(3));
+        SDValue XORReg = XOROp1->getOperand(4);
+        if (!CCValid1 || !CCMask1)
+          return false;
+        int CCValidVal = CCValid1->getZExtValue();
+        int CCMaskVal = CCMask1->getZExtValue();
+        if (combineSRL_IPM_CCMask(XORReg, CCValidVal, CCMaskVal)) {
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uweigand wrote:

Do we really need this recursion here?   It seems to me there should be some way to successively simplify subexpressions.   The common code combiner logic should iterate already, no?

https://github.com/llvm/llvm-project/pull/125970