1 files changed, 67 insertions, 0 deletions
diff --git a/compiler/rustc_codegen_cranelift/src/optimize/peephole.rs b/compiler/rustc_codegen_cranelift/src/optimize/peephole.rs
new file mode 100644
index 000000000..d637b4d89
--- /dev/null
+++ b/compiler/rustc_codegen_cranelift/src/optimize/peephole.rs
@@ -0,0 +1,67 @@
+//! Peephole optimizations that can be performed while creating clif ir.
+
+use cranelift_codegen::ir::{condcodes::IntCC, InstructionData, Opcode, Value, ValueDef};
+use cranelift_frontend::FunctionBuilder;
+
+/// If the given value was produced by a `bint` instruction, return it's input, otherwise return the
+/// given value.
+pub(crate) fn maybe_unwrap_bint(bcx: &mut FunctionBuilder<'_>, arg: Value) -> Value {
+    if let ValueDef::Result(arg_inst, 0) = bcx.func.dfg.value_def(arg) {
+        match bcx.func.dfg[arg_inst] {
+            InstructionData::Unary { opcode: Opcode::Bint, arg } => arg,
+            _ => arg,
+        }
+    } else {
+        arg
+    }
+}
+
+/// If the given value was produced by the lowering of `Rvalue::Not` return the input and true,
+/// otherwise return the given value and false.
+pub(crate) fn maybe_unwrap_bool_not(bcx: &mut FunctionBuilder<'_>, arg: Value) -> (Value, bool) {
+    if let ValueDef::Result(arg_inst, 0) = bcx.func.dfg.value_def(arg) {
+        match bcx.func.dfg[arg_inst] {
+            // This is the lowering of `Rvalue::Not`
+            InstructionData::IntCompareImm {
+                opcode: Opcode::IcmpImm,
+                cond: IntCC::Equal,
+                arg,
+                imm,
+            } if imm.bits() == 0 => (arg, true),
+            _ => (arg, false),
+        }
+    } else {
+        (arg, false)
+    }
+}
+
+/// Returns whether the branch is statically known to be taken or `None` if it isn't statically known.
+pub(crate) fn maybe_known_branch_taken(
+    bcx: &FunctionBuilder<'_>,
+    arg: Value,
+    test_zero: bool,
+) -> Option<bool> {
+    let arg_inst = if let ValueDef::Result(arg_inst, 0) = bcx.func.dfg.value_def(arg) {
+        arg_inst
+    } else {
+        return None;
+    };
+
+    match bcx.func.dfg[arg_inst] {
+        InstructionData::UnaryBool { opcode: Opcode::Bconst, imm } => {
+            if test_zero {
+                Some(!imm)
+            } else {
+                Some(imm)
+            }
+        }
+        InstructionData::UnaryImm { opcode: Opcode::Iconst, imm } => {
+            if test_zero {
+                Some(imm.bits() == 0)
+            } else {
+                Some(imm.bits() != 0)
+            }
+        }
+        _ => None,
+    }
+}