[PATCH] D19369: VirtRegMap.cpp should not just remove an identity copy which also has a impl-def of a super-reg

[Jonas Paulsson via llvm-commits]

jonpa created this revision.
jonpa added a reviewer: qcolombet.
jonpa added a subscriber: llvm-commits.

VirtRegMap removes identity copies, but that leads to machine-verifier complaints if there is a def of a super reg as well.

I am not sure what the best fix is, but the patch attached seems to fix this by transforming the COPY to an IMPLICIT_DEF when there is a def of a super-reg. The patch assumes (arbitrarily) that there could only be one extra operand - not sure if this is always true...

I put this with a testcase on Bugzilla a while ago and would appreciate any review.
https://llvm.org/bugs/show_bug.cgi?id=27156


http://reviews.llvm.org/D19369

Files:
  lib/CodeGen/VirtRegMap.cpp

Index: lib/CodeGen/VirtRegMap.cpp
===================================================================
--- lib/CodeGen/VirtRegMap.cpp
+++ lib/CodeGen/VirtRegMap.cpp
@@ -441,10 +441,25 @@
       if (MI->isIdentityCopy()) {
         ++NumIdCopies;
         DEBUG(dbgs() << "Deleting identity copy.\n");
-        if (Indexes)
-          Indexes->removeMachineInstrFromMaps(*MI);
-        // It's safe to erase MI because MII has already been incremented.
-        MI->eraseFromParent();
+
+        // A COPY which has an implicit def of a super register must
+        // become an IMPLICIT_DEF of that register.
+        if (MI->getNumOperands() > 2) {
+          MachineOperand &MO = MI->getOperand(2);
+          if (MO.isDef() && MO.isImplicit()) {
+            MI->setDesc(TII->get(TargetOpcode::IMPLICIT_DEF));
+            MI->RemoveOperand(0);
+            MI->RemoveOperand(0);
+            MI->getOperand(0).setImplicit(false);
+            assert (MI->getNumOperands() == 1 && "Not a single super reg implicit def?");
+          }
+        }
+        else {
+          if (Indexes)
+            Indexes->removeMachineInstrFromMaps(*MI);
+          // It's safe to erase MI because MII has already been incremented.
+          MI->eraseFromParent();
+        }
       }
     }
   }


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