compiler/rustc_codegen_cranelift/src/optimize/peephole.rs

   1 //! Peephole optimizations that can be performed while creating clif ir.
   2
   3 use cranelift_codegen::ir::{condcodes::IntCC, InstructionData, Opcode, Value, ValueDef};
   4 use cranelift_frontend::FunctionBuilder;
   5
   6 /// If the given value was produced by the lowering of `Rvalue::Not` return the input and true,
   7 /// otherwise return the given value and false.
   8 pub(crate) fn maybe_unwrap_bool_not(bcx: &mut FunctionBuilder<'_>, arg: Value) -> (Value, bool) {
   9     if let ValueDef::Result(arg_inst, 0) = bcx.func.dfg.value_def(arg) {
  10         match bcx.func.dfg[arg_inst] {
  11             // This is the lowering of `Rvalue::Not`
  12             InstructionData::IntCompareImm {
  13                 opcode: Opcode::IcmpImm,
  14                 cond: IntCC::Equal,
  15                 arg,
  16                 imm,
  17             } if imm.bits() == 0 => (arg, true),
  18             _ => (arg, false),
  19         }
  20     } else {
  21         (arg, false)
  22     }
  23 }
  24
  25 /// Returns whether the branch is statically known to be taken or `None` if it isn't statically known.
  26 pub(crate) fn maybe_known_branch_taken(
  27     bcx: &FunctionBuilder<'_>,
  28     arg: Value,
  29     test_zero: bool,
  30 ) -> Option<bool> {
  31     let arg_inst = if let ValueDef::Result(arg_inst, 0) = bcx.func.dfg.value_def(arg) {
  32         arg_inst
  33     } else {
  34         return None;
  35     };
  36
  37     match bcx.func.dfg[arg_inst] {
  38         InstructionData::UnaryImm { opcode: Opcode::Iconst, imm } => {
  39             if test_zero {
  40                 Some(imm.bits() == 0)
  41             } else {
  42                 Some(imm.bits() != 0)
  43             }
  44         }
  45         _ => None,
  46     }
  47 }