MachInst backend: attach SourceLoc span information to all ranges.

Previously, the SourceLoc information transferred in `VCode` only
included PC-spans for non-default SourceLocs. I realized that the
invariant we're supposed to keep here is that every PC is covered; if no
source information, just use `SourceLoc::default()`.

This was spurred by @bjorn3's comment in bytecodealliance#1575 (thanks!).

cranelift/codegen/src/machinst/vcode.rs

@@ -550,7 +550,7 @@ impl<I: VCodeInst> VCode<I> {
  let code_section = sections.get_section(code_idx);
 
  let flags = self.abi.flags();
- let mut cur_srcloc = SourceLoc::default();
+ let mut cur_srcloc = None;
  for &block in &self.final_block_order {
  let new_offset = I::align_basic_block(code_section.cur_offset_from_start());
  while new_offset > code_section.cur_offset_from_start() {
@@ -563,22 +563,20 @@ impl<I: VCodeInst> VCode<I> {
  let (start, end) = self.block_ranges[block as usize];
  for iix in start..end {
  let srcloc = self.srclocs[iix as usize];
- if srcloc != cur_srcloc {
- if !cur_srcloc.is_default() {
+ if Some(srcloc) != cur_srcloc {
+ if cur_srcloc.is_some() {
  code_section.end_srcloc();
  }
- if !srcloc.is_default() {
- code_section.start_srcloc(srcloc);
- }
- cur_srcloc = srcloc;
+ code_section.start_srcloc(srcloc);
+ cur_srcloc = Some(srcloc);
  }
 
  self.insts[iix as usize].emit(code_section, flags);
  }
 
- if !cur_srcloc.is_default() {
+ if cur_srcloc.is_some() {
  code_section.end_srcloc();
- cur_srcloc = SourceLoc::default();
+ cur_srcloc = None;
  }
  }
 

crates/api/src/frame_info.rs

@@ -94,11 +94,7 @@ impl GlobalFrameInfo {
  // the function, because otherwise something is buggy along the way and
  // not accounting for all the instructions. This isn't super critical
  // though so we can omit this check in release mode.
- //
- // FIXME(#1521) aarch64 instruction info isn't quite up-to-par yet.
- if !cfg!(target_arch = "aarch64") {
- debug_assert!(pos.is_some(), "failed to find instruction for {:x}", pc);
- }
+ debug_assert!(pos.is_some(), "failed to find instruction for {:x}", pc);
 
  let instr = match pos {
  Some(pos) => func.instr_map.instructions[pos].srcloc,