[Mips] Simplify isShiftedUIntAtAnyPosition (NFC)

isShiftedUIntAtAnyPosition never gets zero as the argument because the
caller processes ImmValue satisfying isInt<16>(ImmValue), which
includes zero, long before it calls isShiftedUIntAtAnyPosition.

Given that the argument is always nonzero, findFirstSet is identical
to llvm::countr_zero.  Also, x == x >> BitNum << BitNum is always
true, so we are left with:

  isUInt<N>(x >> llvm::countr_zero(x))

Just in case the caller changes its behavior and starts passing zero
to us, we can protect the shift from undefined behavior "x << 64" by
adding "x &&".

diff --git a/llvm/lib/Target/Mips/AsmParser/MipsAsmParser.cpp b/llvm/lib/Target/Mips/AsmParser/MipsAsmParser.cpp
index 45cbddd..bbfeec9 100644 (file)
--- a/llvm/lib/Target/Mips/AsmParser/MipsAsmParser.cpp
+++ b/llvm/lib/Target/Mips/AsmParser/MipsAsmParser.cpp
@@ -2671,9 +2671,7 @@ bool MipsAsmParser::expandJalWithRegs(MCInst &Inst, SMLoc IDLoc,
 
 /// Can the value be represented by a unsigned N-bit value and a shift left?
 template <unsigned N> static bool isShiftedUIntAtAnyPosition(uint64_t x) {
-  unsigned BitNum = findFirstSet(x);
-
-  return (x == x >> BitNum << BitNum) && isUInt<N>(x >> BitNum);
+  return x && isUInt<N>(x >> llvm::countr_zero(x));
 }
 
 /// Load (or add) an immediate into a register.