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

[Ulrich Weigand via cfe-commits]

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@@ -8701,95 +8734,266 @@ SDValue SystemZTargetLowering::combineSETCC(
   return SDValue();
 }
 
-static bool combineCCMask(SDValue &CCReg, int &CCValid, int &CCMask) {
+static std::pair<SDValue, int> findCCUse(const SDValue &Val) {
+  auto *N = Val.getNode();
+  if (!N)
+    return std::make_pair(SDValue(), SystemZ::CCMASK_NONE);
+  switch (N->getOpcode()) {
+  default:
+    return std::make_pair(SDValue(), SystemZ::CCMASK_NONE);
+  case SystemZISD::IPM:
+    if (N->getOperand(0).getOpcode() == SystemZISD::CLC ||
+        N->getOperand(0).getOpcode() == SystemZISD::STRCMP)
+      return std::make_pair(N->getOperand(0), SystemZ::CCMASK_ICMP);
+    return std::make_pair(N->getOperand(0), SystemZ::CCMASK_ANY);
+  case SystemZISD::SELECT_CCMASK: {
+    SDValue Op4CCReg = N->getOperand(4);
+    auto *Op4CCNode = Op4CCReg.getNode();
+    auto *CCValid = dyn_cast<ConstantSDNode>(N->getOperand(2));
+    if (!CCValid || !Op4CCNode)
+      return std::make_pair(SDValue(), SystemZ::CCMASK_NONE);
+    int CCValidVal = CCValid->getZExtValue();
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uweigand wrote:

Looking up the CCValid value can be moved after the ICMP/TM case, we only need it there.

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