[llvm] c50457f - [RISCV] Make the code in MatchSLLIUW ignore the lower bits of the AND mask where the shift has guaranteed zeros.

[Craig Topper via llvm-commits]

Author: Craig Topper
Date: 2021-01-24T00:34:45-08:00
New Revision: c50457f3e4209b0cd0d4a6baa881bac30a9d3016

URL: https://github.com/llvm/llvm-project/commit/c50457f3e4209b0cd0d4a6baa881bac30a9d3016
DIFF: https://github.com/llvm/llvm-project/commit/c50457f3e4209b0cd0d4a6baa881bac30a9d3016.diff

LOG: [RISCV] Make the code in MatchSLLIUW ignore the lower bits of the AND mask where the shift has guaranteed zeros.

This avoids being dependent on SimplifyDemandedBits having cleared
those bits.

It could make sense to teach SimplifyDemandedBits to keep all
lower bits 1 in an AND mask when possible. This could be
implemented with slli+srli in the general case rather than
needing to materialize the constant.

Added: 
    

Modified: 
    llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp b/llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
index 078ed1b8d8d1..2198b275ec11 100644
--- a/llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
@@ -871,7 +871,7 @@ bool RISCVDAGToDAGISel::MatchSLLIUW(SDNode *N) const {
 
   // Immediate range should be enforced by uimm5 predicate.
   assert(VC2 < 32 && "Unexpected immediate");
-  return VC1 == ((uint64_t)0xFFFFFFFF << VC2);
+  return (VC1 >> VC2) == UINT64_C(0xFFFFFFFF);
 }
 
 bool RISCVDAGToDAGISel::selectVSplat(SDValue N, SDValue &SplatVal) {