[llvm] [InlineSpiller] Check rematerialization before folding operand (PR #134015)

[Matt Arsenault via llvm-commits]

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@@ -615,6 +620,23 @@ bool InlineSpiller::canGuaranteeAssignmentAfterRemat(Register VReg,
   return true;
 }
 
+/// hasPhysRegAvailable - Check if there is an available physical register for
+/// rematerialization.
+bool InlineSpiller::hasPhysRegAvailable(const MachineInstr &MI) {
+  if (!Order || !Matrix)
+    return false;
+
+  SlotIndex UseIdx = LIS.getInstructionIndex(MI).getRegSlot(true);
+  SlotIndex PrevIdx = UseIdx.getPrevSlot();
+
+  for (MCPhysReg PhysReg : *Order) {
+    if (!Matrix->checkInterference(PrevIdx, UseIdx, PhysReg))
+      return true;
+  }
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arsenm wrote:

The inline spiller should not be doing full availability checks. This is algorithmically really bad. The existing tryAssign loop is bad enough

https://github.com/llvm/llvm-project/pull/134015