x64: Shrink Inst from 72 to 48 bytes (#4514)

https://github.com/bytecodealliance/wasmtime/pull/4514

cranelift/codegen/src/isa/aarch64/inst.isle

@@ -854,6 +854,7 @@
 (type BranchTarget (primitive BranchTarget))
 (type BoxJTSequenceInfo (primitive BoxJTSequenceInfo))
 (type CodeOffset (primitive CodeOffset))
+(type VecMachLabel extern (enum))
 
 (type ExtendOp extern
   (enum

cranelift/codegen/src/isa/s390x/inst.isle

@@ -880,6 +880,7 @@
 (type BoxCallInfo (primitive BoxCallInfo))
 (type BoxCallIndInfo (primitive BoxCallIndInfo))
 (type BoxJTSequenceInfo (primitive BoxJTSequenceInfo))
+(type VecMachLabel extern (enum))
 
 ;; An ALU operation.
 (type ALUOp

cranelift/codegen/src/isa/x64/inst.isle

@@ -371,8 +371,7 @@
                     (tmp1 WritableReg)
                     (tmp2 WritableReg)
                     (default_target MachLabel)
-                    (targets VecMachLabel)
-                    (targets_for_term VecMachLabel))
+                    (targets BoxVecMachLabel))
 
        ;; Indirect jump: jmpq (reg mem).
        (JmpUnknown (target RegMem))
@@ -504,6 +503,8 @@
 
 (type BoxCallInfo extern (enum))
 
+(type BoxVecMachLabel extern (enum))
+
 ;; Get the `OperandSize` for a given `Type`, rounding smaller types up to 32 bits.
 (decl operand_size_of_type_32_64 (Type) OperandSize)
 (extern constructor operand_size_of_type_32_64 operand_size_of_type_32_64)

cranelift/codegen/src/isa/x64/inst/mod.rs

@@ -48,7 +48,7 @@ pub struct CallInfo {
 fn inst_size_test() {
     // This test will help with unintentionally growing the size
     // of the Inst enum.
-    assert_eq!(72, std::mem::size_of::<Inst>());
+    assert_eq!(48, std::mem::size_of::<Inst>());
 }
 
 pub(crate) fn low32_will_sign_extend_to_64(x: u64) -> bool {

cranelift/codegen/src/isa/x64/lower.rs

@@ -17,7 +17,7 @@ use crate::machinst::lower::*;
 use crate::machinst::*;
 use crate::result::CodegenResult;
 use crate::settings::{Flags, TlsModel};
-use alloc::vec::Vec;
+use alloc::boxed::Box;
 use log::trace;
 use smallvec::SmallVec;
 use std::convert::TryFrom;
@@ -3236,10 +3236,10 @@ impl LowerBackend for X64Backend {
                     };
                     ctx.emit(Inst::cmp_rmi_r(cmp_size, RegMemImm::imm(jt_size), idx));
 
-                    let targets_for_term: Vec<MachLabel> = targets.to_vec();
                     let default_target = targets[0];
 
-                    let jt_targets: Vec<MachLabel> = targets.iter().skip(1).cloned().collect();
+                    let jt_targets: Box<SmallVec<[MachLabel; 4]>> =
+                        Box::new(targets.iter().skip(1).cloned().collect());
 
                     ctx.emit(Inst::JmpTableSeq {
                         idx,
@@ -3247,7 +3247,6 @@ impl LowerBackend for X64Backend {
                         tmp2,
                         default_target,
                         targets: jt_targets,
-                        targets_for_term,
                     });
                 }
 

cranelift/codegen/src/isa/x64/lower/isle.rs

@@ -30,10 +30,12 @@ use crate::{
         VCodeConstantData,
     },
 };
+use smallvec::SmallVec;
 use std::boxed::Box;
 use std::convert::TryFrom;
 
 type BoxCallInfo = Box<CallInfo>;
+type BoxVecMachLabel = Box<SmallVec<[MachLabel; 4]>>;
 
 pub struct SinkableLoad {
     inst: Inst,

cranelift/codegen/src/machinst/isle.rs

@@ -25,7 +25,6 @@ pub type ValueRegs = crate::machinst::ValueRegs<Reg>;
 pub type WritableValueRegs = crate::machinst::ValueRegs<WritableReg>;
 pub type InstOutput = SmallVec<[ValueRegs; 2]>;
 pub type InstOutputBuilder = Cell<InstOutput>;
-pub type VecMachLabel = Vec<MachLabel>;
 pub type BoxExternalName = Box<ExternalName>;
 pub type Range = (usize, usize);
 

cranelift/codegen/src/prelude.isle

@@ -195,7 +195,6 @@
 ;;;; Common Mach Types ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (type MachLabel (primitive MachLabel))
-(type VecMachLabel extern (enum))
 (type ValueLabel (primitive ValueLabel))
 (type UnwindInst (primitive UnwindInst))
 (type ExternalName (primitive ExternalName))