[PATCH] D135700: [DAGCombine] Simplify (truncate (build_pair x, y)) -> (truncate x) or x

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:13508
+  if (N0.getOpcode() == ISD::BUILD_PAIR) {
+    // if we match the low element of the pair, just return it.
+    if (N0.getOperand(0).getValueType() == VT)
----------------
Capitalize


================
Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:13511
+      return N0.getOperand(0);
+    // otherwise, if the low part is still too large, apply the truncate.
+    if (N0.getOperand(0).getValueType().bitsGT(VT))
----------------
Capitalize 


================
Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:13513
+    if (N0.getOperand(0).getValueType().bitsGT(VT))
+      return DAG.getNode(ISD::TRUNCATE, SDLoc(N), VT, N0.getOperand(0));
+  }
----------------
Can just unconditionally truncate, it folds out the equality case for you


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D135700/new/

https://reviews.llvm.org/D135700