[llvm] [x86] Enable indirect tail calls with more arguments (PR #137643)

[Eli Friedman via llvm-commits]

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@@ -890,27 +890,50 @@ static bool isCalleeLoad(SDValue Callee, SDValue &Chain, bool HasCallSeq) {
       LD->getExtensionType() != ISD::NON_EXTLOAD)
     return false;
 
+  // If the load's outgoing chain has more than one use, we can't (currently)
+  // move the load since we'd most likely create a loop. TODO: Maybe it could
+  // work if moveBelowOrigChain() updated *all* the chain users.
+  if (!Callee.getValue(1).hasOneUse())
+    return false;
+
   // Now let's find the callseq_start.
   while (HasCallSeq && Chain.getOpcode() != ISD::CALLSEQ_START) {
     if (!Chain.hasOneUse())
       return false;
     Chain = Chain.getOperand(0);
   }
 
-  if (!Chain.getNumOperands())
-    return false;
-  // Since we are not checking for AA here, conservatively abort if the chain
-  // writes to memory. It's not safe to move the callee (a load) across a store.
-  if (isa<MemSDNode>(Chain.getNode()) &&
-      cast<MemSDNode>(Chain.getNode())->writeMem())
+  while (true) {
+    if (!Chain.getNumOperands())
+      return false;
+    // Since we are not checking for AA here, conservatively abort if the chain
+    // writes to memory. It's not safe to move the callee (a load) across a
+    // store.
+    if (isa<MemSDNode>(Chain.getNode()) &&
+        cast<MemSDNode>(Chain.getNode())->writeMem())
+      return false;
+    // Moving across inline asm is not safe: it could do anything.
+    if (Chain.getNode()->getOpcode() == ISD::INLINEASM ||
+        Chain.getNode()->getOpcode() == ISD::INLINEASM_BR)
+      return false;
----------------
efriedma-quic wrote:

Please just allow specific nodes, and forbid anything unknown.  Trying to list out every possible relevant node is guaranteed to fall out of date at some point, even if you manage to come up with a complete list.

https://github.com/llvm/llvm-project/pull/137643