[PATCH] D14966: LiveIntervalAnalysis: Add function to reassign vregs of dead subregister defs

[Andrew Trick via llvm-commits]

atrick requested changes to this revision.
atrick added a comment.
This revision now requires changes to proceed.

LGTM except for the inline comments.


================
Comment at: lib/CodeGen/LiveIntervalAnalysis.cpp:1481
@@ +1480,3 @@
+
+void LiveIntervals::renameDeadSubRegDefs() {
+  for (size_t I = 0, E = MRI->getNumVirtRegs(); I < E; ++I) {
----------------
This function needs comments reflecting some of what is explained in the commit message. It should be clear that this is an optimization not required for correctness.

================
Comment at: lib/CodeGen/LiveIntervalAnalysis.cpp:1498
@@ +1497,3 @@
+      SlotIndex Def = VNI->def;
+      unsigned Reg = LI->reg;
+      // Do we only have dead (subregister) defs at VNI->def?
----------------
This shadows 'Reg' above. It should probably be an assert.

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Comment at: lib/CodeGen/LiveIntervalAnalysis.cpp:1528
@@ +1527,3 @@
+        MO.setReg(NewVReg);
+        MO.setIsUndef();
+        MO.setIsDead();
----------------
setIsUndef confused me at first. You must be assuming here that this is a subregister def and that subreg defs are always marked undef. Please comment. Also let me know where that invariant is explained and enforced.


Repository:
  rL LLVM

http://reviews.llvm.org/D14966