[llvm] [RegAlloc] Trace through COPYs to find rematerializable definitions (PR #190955)

[Romanov Vlad via llvm-commits]

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@@ -680,10 +680,36 @@ bool InlineSpiller::reMaterializeFor(LiveInterval &VirtReg, MachineInstr &MI) {
   // live interval; this happens if we rematted to all uses, and
   // then further split one of those live ranges.
   if (!DefMI) {
-    markValueUsed(&VirtReg, ParentVNI);
-    LLVM_DEBUG(dbgs() << "\tcannot remat missing def for " << UseIdx << '\t'
-                      << MI);
-    return false;
+    // Try to find the rematerializable definition by tracing through COPY
+    // chains.
+    MachineInstr *CurDef = MRI.getUniqueVRegDef(VirtReg.reg());
+    LLVM_DEBUG(dbgs() << "\ttracing COPY chain from "
+                      << printReg(VirtReg.reg(), &TRI) << ", initial def: "
+                      << (CurDef ? TII.getName(CurDef->getOpcode()) : "null")
+                      << "\n");
+    while (CurDef && CurDef->isCopy() && !CurDef->getOperand(0).getSubReg() &&
+           !CurDef->getOperand(1).getSubReg()) {
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romanovvlad wrote:

Thanks! Using isFullCopy now.

https://github.com/llvm/llvm-project/pull/190955