[PATCH] D30379: [SelectionDAG] Make SelectionDAG aware of the known bits in UADDO and SADDO.

[Simon Pilgrim via Phabricator via llvm-commits]

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

LGTM with a couple of minors



================
Comment at: lib/CodeGen/SelectionDAG/SelectionDAG.cpp:2579
 
-    // With ADDE, a carry bit may be added in, so we can only use this
-    // information if we know (at least) that the low two bits are clear.  We
-    // then return to the caller that the low bit is unknown but that other bits
-    // are known zero.
-    if (KnownZeroLow >= 2) // ADDE
-      KnownZero |= APInt::getBitsSet(BitWidth, 1, KnownZeroLow);
+    KnownZero.setBits(0, KnownZeroLow);
+    if (KnownZeroHigh > 1)
----------------
KnownZero.setLowBits ?


================
Comment at: lib/CodeGen/SelectionDAG/SelectionDAG.cpp:2581
+    if (KnownZeroHigh > 1)
+      KnownZero.setBits(BitWidth - KnownZeroHigh + 1, BitWidth);
     break;
----------------
KnownZero.setHighBits ?


https://reviews.llvm.org/D30379