[PATCH] D127996: [RISCV] Delete dead elideCopy code in InsertVSETVLI [nfc]

[Philip Reames via Phabricator via llvm-commits]

reames created this revision.
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This code appears to be dead.  A simple whole register copy of an IMPLICIT_DEF, is simply an IMPLICIT_DEF of it's own.  (This would not be true for freeze, but is for copy.)

If we find a case which gets here with vector operand copy of an IMPLICIT_DEF, we most likely have an earlier missed optimization anyways.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D127996

Files:
  llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp


Index: llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp
===================================================================
--- llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp
+++ llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp
@@ -780,19 +780,6 @@
   return RISCV::X0 == MI.getOperand(0).getReg();
 }
 
-static MachineInstr *elideCopies(MachineInstr *MI,
-                                 const MachineRegisterInfo *MRI) {
-  while (true) {
-    if (!MI->isFullCopy())
-      return MI;
-    if (!Register::isVirtualRegister(MI->getOperand(1).getReg()))
-      return nullptr;
-    MI = MRI->getVRegDef(MI->getOperand(1).getReg());
-    if (!MI)
-      return nullptr;
-  }
-}
-
 static VSETVLIInfo computeInfoForInstr(const MachineInstr &MI, uint64_t TSFlags,
                                        const MachineRegisterInfo *MRI) {
   VSETVLIInfo InstrInfo;
@@ -828,13 +815,10 @@
     // If the tied operand is an IMPLICIT_DEF we can keep TailAgnostic.
     const MachineOperand &UseMO = MI.getOperand(UseOpIdx);
     MachineInstr *UseMI = MRI->getVRegDef(UseMO.getReg());
-    if (UseMI) {
-      UseMI = elideCopies(UseMI, MRI);
-      if (UseMI && UseMI->isImplicitDef()) {
-        TailAgnostic = true;
-        if (UsesMaskPolicy)
-          MaskAgnostic = true;
-      }
+    if (UseMI && UseMI->isImplicitDef()) {
+      TailAgnostic = true;
+      if (UsesMaskPolicy)
+        MaskAgnostic = true;
     }
     // Some pseudo instructions force a tail agnostic policy despite having a
     // tied def.


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