[llvm] [MachineScheduler] Fix physreg dependencies of ExitSU (PR #123541)

[Sergei Barannikov via llvm-commits]

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@@ -209,13 +209,25 @@ void ScheduleDAGInstrs::addSchedBarrierDeps() {
   ExitSU.setInstr(ExitMI);
   // Add dependencies on the defs and uses of the instruction.
   if (ExitMI) {
+    const MCInstrDesc &MIDesc = ExitMI->getDesc();
     for (const MachineOperand &MO : ExitMI->all_uses()) {
+      unsigned OpIdx = MO.getOperandNo();
       Register Reg = MO.getReg();
       if (Reg.isPhysical()) {
+        // addPhysRegDataDeps uses the provided operand index to retrieve
+        // the operand use cycle from the scheduling model. If the operand
+        // is "fake" (e.g., an operand of a call instruction used to pass
+        // an argument to the called function.), the scheduling model may not
+        // have an entry for it. If this is the case, pass -1 as operand index,
+        // which will cause addPhysRegDataDeps to add an artificial dependency.
+        // FIXME: Using hasImplicitUseOfPhysReg here is inaccurate as it misses
+        //  aliases. When fixing, make sure to update addPhysRegDataDeps, too.
+        bool IsRealUse = OpIdx < MIDesc.getNumOperands() ||
+                         MIDesc.hasImplicitUseOfPhysReg(Reg);
         for (MCRegUnit Unit : TRI->regunits(Reg))
-          Uses.insert(PhysRegSUOper(&ExitSU, -1, Unit));
+          Uses.insert(PhysRegSUOper(&ExitSU, IsRealUse ? OpIdx : -1, Unit));
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s-barannikov wrote:

This is where an operand index gets a negative value. There is one more place at the end of this function.


https://github.com/llvm/llvm-project/pull/123541