cranelift: Introduce a feature to enable trace logs (#4484)

* Don't use `log::trace` directly but a feature-enabled `trace` macro
* Don't emit disassembly based on the log level

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

@@ -2789,7 +2789,7 @@ pub(crate) fn emit(
         }
 
         Inst::VirtualSPOffsetAdj { offset } => {
-            log::trace!(
+            trace!(
                 "virtual sp offset adjusted by {} -> {}",
                 offset,
                 state.virtual_sp_offset + offset

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

@@ -6,7 +6,7 @@ use crate::isa::x64::abi::X64ABIMachineSpec;
 use crate::isa::x64::inst::regs::pretty_print_reg;
 use crate::isa::x64::settings as x64_settings;
 use crate::isa::CallConv;
-use crate::machinst::*;
+use crate::{machinst::*, trace};
 use crate::{settings, CodegenError, CodegenResult};
 use alloc::boxed::Box;
 use alloc::vec::Vec;
@@ -2236,7 +2236,7 @@ impl MachInst for Inst {
     }
 
     fn gen_move(dst_reg: Writable<Reg>, src_reg: Reg, ty: Type) -> Inst {
-        log::trace!(
+        trace!(
             "Inst::gen_move {:?} -> {:?} (type: {:?})",
             src_reg,
             dst_reg.to_reg(),

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

@@ -14,11 +14,10 @@ use crate::isa::x64::inst::args::*;
 use crate::isa::x64::inst::*;
 use crate::isa::{x64::settings as x64_settings, x64::X64Backend, CallConv};
 use crate::machinst::lower::*;
-use crate::machinst::*;
 use crate::result::CodegenResult;
 use crate::settings::{Flags, TlsModel};
+use crate::{machinst::*, trace};
 use alloc::boxed::Box;
-use log::trace;
 use smallvec::SmallVec;
 use std::convert::TryFrom;
 use target_lexicon::Triple;

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

@@ -67,7 +67,6 @@ impl TargetIsa for X64Backend {
         let flags = self.flags();
         let (vcode, regalloc_result) = self.compile_vcode(func, flags.clone())?;
 
-        let want_disasm = want_disasm || log::log_enabled!(log::Level::Debug);
         let emit_result = vcode.emit(&regalloc_result, want_disasm, flags.machine_code_cfg_info());
         let frame_size = emit_result.frame_size;
         let value_labels_ranges = emit_result.value_labels_ranges;