[llvm] 30080b0 - [DAGCombiner] Minor compile time improvement to (sext_in_reg (sign_extend_vector_inreg x)) optimization.

[Craig Topper via llvm-commits]

Author: Craig Topper
Date: 2021-03-21T11:16:41-07:00
New Revision: 30080b003e75969155b5baa993b6ffdab602a5ff

URL: https://github.com/llvm/llvm-project/commit/30080b003e75969155b5baa993b6ffdab602a5ff
DIFF: https://github.com/llvm/llvm-project/commit/30080b003e75969155b5baa993b6ffdab602a5ff.diff

LOG: [DAGCombiner] Minor compile time improvement to (sext_in_reg (sign_extend_vector_inreg x)) optimization.

Don't bother calling ComputeNumSignBits if N00Bits < ExtVTBits. No
matter what answer we get back this will be true:
(N00Bits - DAG.ComputeNumSignBits(N00, DemandedSrcElts)) < ExtVTBits)

So we might as well save the computation. This makes the code more
consistent with the similar (sext_in_reg (sext x)) handling above.

Added: 
    

Modified: 
    llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

Removed: 
    


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diff  --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 2f3826e45419..e5112cdcd417 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -11799,8 +11799,9 @@ SDValue DAGCombiner::visitSIGN_EXTEND_INREG(SDNode *N) {
     bool IsZext = N0.getOpcode() == ISD::ZERO_EXTEND_VECTOR_INREG;
     APInt DemandedSrcElts = APInt::getLowBitsSet(SrcElts, DstElts);
     if ((N00Bits == ExtVTBits ||
-         (!IsZext && (N00Bits - DAG.ComputeNumSignBits(N00, DemandedSrcElts)) <
-                         ExtVTBits)) &&
+         (!IsZext && (N00Bits < ExtVTBits ||
+                      (N00Bits - DAG.ComputeNumSignBits(N00, DemandedSrcElts)) <
+                          ExtVTBits))) &&
         (!LegalOperations ||
          TLI.isOperationLegal(ISD::SIGN_EXTEND_VECTOR_INREG, VT)))
       return DAG.getNode(ISD::SIGN_EXTEND_VECTOR_INREG, SDLoc(N), VT, N00);