[PATCH] D18448: Fix Sub-register Rewriting in Aggressive Anti-Dependence Breaker

[Hal Finkel via llvm-commits]

hfinkel accepted this revision.
hfinkel added a comment.
This revision is now accepted and ready to land.

LGTM, thanks! -- Nice efficient patch :-)  [I realize that I'm ruining that somewhat by asking for a comment ;) ]


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Comment at: ../llvm/lib/CodeGen/AggressiveAntiDepBreaker.cpp:315
@@ -314,14 +314,3 @@
     DEBUG(dbgs() << "->g" << State->GetGroup(Reg) << tag);
-  }
-  // Repeat for subregisters.
-  for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
-    unsigned SubregReg = *SubRegs;
-    if (!State->IsLive(SubregReg)) {
-      KillIndices[SubregReg] = KillIdx;
-      DefIndices[SubregReg] = ~0u;
-      RegRefs.erase(SubregReg);
-      State->LeaveGroup(SubregReg);
-      DEBUG(if (header) {
-          dbgs() << header << TRI->getName(Reg); header = nullptr; });
-      DEBUG(dbgs() << " " << TRI->getName(SubregReg) << "->g" <<
-            State->GetGroup(SubregReg) << tag);
+    // Repeat for subregisters.
+    for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
----------------
Please add a comment here explaining why we do this only if the superregister was not live. Maybe something like this:

// Note that we only do this if the superregister was not live because otherwise, regardless whether we have an explicit use of the subregister, the subregister's contents are needed for the uses of the superregister.


http://reviews.llvm.org/D18448