[RISCV] Make shouldConvertConstantLoadToIntImm return true unless enableUnalignedScalarMem is true.

This restores the old behavior before D129402 when
enableUnalignedScalarMem is false. This fixes a regression spotted
by @asb.

To fix this correctly, we need to consider alignment of the load
we'd be replacing, but that's not possible in the current interface.

Author: topperc

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -1174,6 +1174,13 @@ bool RISCVTargetLowering::shouldConvertConstantLoadToIntImm(const APInt &Imm,
   if (isInt<32>(Val))
     return true;
 
+  // A constant pool entry may be more aligned thant he load we're trying to
+  // replace. If we don't support unaligned scalar mem, prefer the constant
+  // pool.
+  // TODO: Can the caller pass down the alignment?
+  if (!Subtarget.enableUnalignedScalarMem())
+    return true;
+
   // Prefer to keep the load if it would require many instructions.
   // This uses the same threshold we use for constant pools but doesn't
   // check useConstantPoolForLargeInts.