[llvm] [X86] Reuse already-materialized values when forming LEAs (alternative) (PR #210739)

[Nikita Taranov via llvm-commits]

================
@@ -2061,22 +2067,90 @@ bool X86DAGToDAGISel::matchAddress(SDValue N, X86ISelAddressMode &AM) {
   return false;
 }
 
+// Returns true if V has a use that materializes it in a register as a value -
+// a stored value operand or a CopyToReg (a return value, call argument, or a
+// value that is live out of the block). Such a use means V will be in a
+// register regardless, so reusing it when forming an LEA is free. Uses where V
+// is only an address (a load/store pointer, or folded into another address
+// computation) do not materialize it. This is a more precise replacement for
+// the !hasOneUse() proxy: an address-only multi-use value is not materialized.
+bool X86DAGToDAGISel::hasMaterializingUse(SDValue V) const {
+  const TargetInstrInfo *TII = Subtarget->getInstrInfo();
+  for (SDUse &U : V->uses()) {
+    if (U.getResNo() != V.getResNo())
+      continue;
+    SDNode *User = U.getUser();
+    // A return value, call argument, or a value live out of the block.
+    if (User->getOpcode() == ISD::CopyToReg)
+      return true;
+    // A stored value materializes V (V as a store *address* does not).
+    if (auto *St = dyn_cast<StoreSDNode>(User)) {
+      if (St->getValue() == V)
+        return true;
+      continue;
+    }
+    // Selection may already have turned the ISD::STORE into a machine store by
+    // the time we get here. For a store the memory reference comes first, so
+    // the stored value is the operand at X86::AddrNumOperands (as in e.g.
+    // X86AvoidStoreForwardingBlocks). Note there is no getOperandBias() here:
+    // unlike a MachineInstr, an SDNode's operand list has no leading defs.
+    if (User->isMachineOpcode() &&
+        TII->get(User->getMachineOpcode()).mayStore() &&
+        User->getNumOperands() > X86::AddrNumOperands &&
+        User->getOperand(X86::AddrNumOperands) == V)
----------------
nickitat wrote:

Pls check the new version

https://github.com/llvm/llvm-project/pull/210739