[SystemZ] Use llvm::countl_zero and llvm::countr_zero (NFC)

isVectorConstantLegal calls findFirstSet and findLastSet, but we don't
rely on their ability to return std::numeric_limits<T>::max() on input
0.

This patch replaces those calls with calls to llvm::countl_zero and
llvm::countr_zero.

Due to an off-by-one error in the original code, the value of Upper
could change at bit N, where N is the index of the highest set bit in
SplatBitsZ, but the difference doesn't matter at the end.  Without
this patch, Upper could have bit N set.  With this patch, Upper never
has bit N set.  Either way, both calls to tryValue have this bit set
because the argument is ORed with SplatBitsZ.

diff --git a/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp b/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
index 5dca792..7590bef 100644 (file)
--- a/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
@@ -781,10 +781,10 @@ bool SystemZVectorConstantInfo::isVectorConstantLegal(
   // IMMEDIATE or a wraparound mask in VECTOR GENERATE MASK.
   uint64_t SplatBitsZ = SplatBits.getZExtValue();
   uint64_t SplatUndefZ = SplatUndef.getZExtValue();
-  uint64_t Lower =
-      (SplatUndefZ & ((uint64_t(1) << findFirstSet(SplatBitsZ)) - 1));
-  uint64_t Upper =
-      (SplatUndefZ & ~((uint64_t(1) << findLastSet(SplatBitsZ)) - 1));
+  unsigned LowerBits = llvm::countr_zero(SplatBitsZ);
+  unsigned UpperBits = llvm::countl_zero(SplatBitsZ);
+  uint64_t Lower = SplatUndefZ & maskTrailingOnes<uint64_t>(LowerBits);
+  uint64_t Upper = SplatUndefZ & maskLeadingOnes<uint64_t>(UpperBits);
   if (tryValue(SplatBitsZ | Upper | Lower))
     return true;