Emit compressed instruction encodings for instructions where constraints allow

cranelift/filetests/isa/intel/binary64.cton

@@ -1,6 +1,7 @@
 ; binary emission of 64-bit code.
 test binemit
 set is_64bit
+set is_compressed
 isa intel haswell
 
 ; The binary encodings can be verified with the command:

cranelift/src/filetest/binemit.rs

@@ -104,16 +104,32 @@ impl SubTest for TestBinEmit {
         // value locations. The current error reporting is just crashing...
         let mut func = func.into_owned();
 
+        let is_compressed = isa.flags().is_compressed();
+
         // Give an encoding to any instruction that doesn't already have one.
         for ebb in func.layout.ebbs() {
             for inst in func.layout.ebb_insts(ebb) {
                 if !func.encodings[inst].is_legal() {
-                    if let Ok(enc) = isa.encode(
+                    let mut legal_encodings = isa.legal_encodings(
                         &func.dfg,
                         &func.dfg[inst],
                         func.dfg.ctrl_typevar(inst),
-                    )
-                    {
+                    );
+
+                    let enc = if is_compressed {
+                        // Get the smallest legal encoding
+                        legal_encodings
+                            .filter(|e| {
+                                let recipe_constraints = &encinfo.constraints[e.recipe()];
+                                recipe_constraints.satisfied(inst, &func)
+                            })
+                            .min_by_key(|&e| encinfo.bytes(e))
+                    } else {
+                        // If not using compressed, just use the first encoding.
+                        legal_encodings.next()
+                    };
+
+                    if let Some(enc) = enc {
                         func.encodings[inst] = enc;
                     }
                 }

lib/cretonne/meta/isa/intel/recipes.py

@@ -13,7 +13,7 @@ from .registers import GPR, ABCD, FPR
 try:
     from typing import Tuple, Dict  # noqa
     from cdsl.instructions import InstructionFormat  # noqa
-    from cdsl.isa import ConstraintSeq, BranchRange, PredNode  # noqa
+    from cdsl.isa import ConstraintSeq, BranchRange, PredNode, OperandConstraint  # noqa
 except ImportError:
     pass
 

lib/cretonne/src/isa/constraints.rs

@@ -9,6 +9,7 @@
 
 use binemit::CodeOffset;
 use isa::{RegClass, RegUnit};
+use ir::{Function, ValueLoc, Inst};
 
 /// Register constraint for a single value operand or instruction result.
 pub struct OperandConstraint {
@@ -21,6 +22,34 @@ pub struct OperandConstraint {
     pub regclass: RegClass,
 }
 
+impl OperandConstraint {
+    /// Check if this operand constraint is satisfied by the given value location.
+    /// For tied constraints, this only checks the register class, not that the
+    /// counterpart operand has the same value location.
+    pub fn satisfied(&self, loc: ValueLoc) -> bool {
+        match self.kind {
+            ConstraintKind::Reg |
+            ConstraintKind::Tied(_) => {
+                if let ValueLoc::Reg(reg) = loc {
+                    self.regclass.contains(reg)
+                } else {
+                    false
+                }
+            }
+            ConstraintKind::FixedReg(reg) => {
+                loc == ValueLoc::Reg(reg) && self.regclass.contains(reg)
+            }
+            ConstraintKind::Stack => {
+                if let ValueLoc::Stack(_) = loc {
+                    true
+                } else {
+                    false
+                }
+            }
+        }
+    }
+}
+
 /// The different kinds of operand constraints.
 #[derive(Clone, Copy, PartialEq, Eq)]
 pub enum ConstraintKind {
@@ -78,6 +107,36 @@ pub struct RecipeConstraints {
     pub tied_ops: bool,
 }
 
+impl RecipeConstraints {
+    /// Check that these constraints are satisfied by the operands on `inst`.
+    pub fn satisfied(&self, inst: Inst, func: &Function) -> bool {
+        for (&arg, constraint) in func.dfg.inst_args(inst).iter().zip(self.ins) {
+            let loc = func.locations[arg];
+
+            if let ConstraintKind::Tied(out_index) = constraint.kind {
+                let out_val = func.dfg.inst_results(inst)[out_index as usize];
+                let out_loc = func.locations[out_val];
+                if loc != out_loc {
+                    return false;
+                }
+            }
+
+            if !constraint.satisfied(loc) {
+                return false;
+            }
+        }
+
+        for (&arg, constraint) in func.dfg.inst_results(inst).iter().zip(self.outs) {
+            let loc = func.locations[arg];
+            if !constraint.satisfied(loc) {
+                return false;
+            }
+        }
+
+        true
+    }
+}
+
 /// Constraints on the range of a branch instruction.
 ///
 /// A branch instruction usually encodes its destination as a signed n-bit offset from an origin.