From a76e0e8aa57220fe9c75f810c293ba2694d65e7a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sa=C3=BAl=20Cabrera?= <saulecabrera@gmail.com>
Date: Tue, 13 Dec 2022 07:13:45 -0500
Subject: [PATCH] Decouple `MachBufferFinalized<Stencil>` from
 `ir::FunctionParameters` (#5419)

This commit allows retrieving a `MachBufferFinalized<Final>` from a
`MachBufferFinalized<Stencil>` without relying on
`ir::FunctionParameters`. Instead it uses the function's base source location,
which is the only piece used by the previous `apply_params` definition.

This change allows other uses cases (e.g. Winch) to use an opaque, common
concept, exposed outside of `cranelift-codegen` to get the finalized state of
the machine buffer. This change implies that Winch will transitively know about
the `Stencil` compilation phase, but the `Stencil` phase is not exposed to Winch.

Other alternatives considered:

Parametrizing `MachBufferFinzalized` in a way such that it allows specifying
which compilation phase the caller is targetting. Such approach would require
also parametrizing the `MachSrcLoc` definition. One of the main drawbacks of
this approach is that it also requires changing how the `MachBuffer`'s
`start_srcloc` works: for caller requesting a `Final` `MachBufferFinalized`, the
`MachBuffer` will need to work in terms of `SourceLoc` rather than in
`RelSourceLoc` terms. This approach doesn't necessarily present more advantages
than the approach presented in this change, in which there's no need to make any
fundamental changes and in which all the `cranelift-codegen` primitives are
already exposed.
---
 cranelift/codegen/src/machinst/buffer.rs | 12 +++++-------
 cranelift/codegen/src/machinst/mod.rs    |  2 +-
 2 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/cranelift/codegen/src/machinst/buffer.rs b/cranelift/codegen/src/machinst/buffer.rs
index 8a71d33cbc..316e916db3 100644
--- a/cranelift/codegen/src/machinst/buffer.rs
+++ b/cranelift/codegen/src/machinst/buffer.rs
@@ -141,7 +141,6 @@
 //! semantics below (grep for "Preserves execution semantics").
 
 use crate::binemit::{Addend, CodeOffset, Reloc, StackMap};
-use crate::ir::function::FunctionParameters;
 use crate::ir::{ExternalName, Opcode, RelSourceLoc, SourceLoc, TrapCode};
 use crate::isa::unwind::UnwindInst;
 use crate::machinst::{
@@ -172,8 +171,6 @@ pub trait CompilePhase {
 }
 
 /// Status of a compiled artifact that needs patching before being used.
-///
-/// Only used internally.
 #[derive(Clone, Debug, PartialEq)]
 #[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]
 pub struct Stencil;
@@ -267,7 +264,8 @@ pub struct MachBuffer<I: VCodeInst> {
 }
 
 impl MachBufferFinalized<Stencil> {
-    pub(crate) fn apply_params(self, params: &FunctionParameters) -> MachBufferFinalized<Final> {
+    /// Get a finalized machine buffer by applying the function's base source location.
+    pub fn apply_base_srcloc(self, base_srcloc: SourceLoc) -> MachBufferFinalized<Final> {
         MachBufferFinalized {
             data: self.data,
             relocs: self.relocs,
@@ -276,7 +274,7 @@ impl MachBufferFinalized<Stencil> {
             srclocs: self
                 .srclocs
                 .into_iter()
-                .map(|srcloc| srcloc.apply_params(params))
+                .map(|srcloc| srcloc.apply_base_srcloc(base_srcloc))
                 .collect(),
             stack_maps: self.stack_maps,
             unwind_info: self.unwind_info,
@@ -1550,11 +1548,11 @@ pub struct MachSrcLoc<T: CompilePhase> {
 }
 
 impl MachSrcLoc<Stencil> {
-    fn apply_params(self, params: &FunctionParameters) -> MachSrcLoc<Final> {
+    fn apply_base_srcloc(self, base_srcloc: SourceLoc) -> MachSrcLoc<Final> {
         MachSrcLoc {
             start: self.start,
             end: self.end,
-            loc: self.loc.expand(params.base_srcloc()),
+            loc: self.loc.expand(base_srcloc),
         }
     }
 }
diff --git a/cranelift/codegen/src/machinst/mod.rs b/cranelift/codegen/src/machinst/mod.rs
index c08274c709..37f617fd6a 100644
--- a/cranelift/codegen/src/machinst/mod.rs
+++ b/cranelift/codegen/src/machinst/mod.rs
@@ -323,7 +323,7 @@ impl CompiledCodeStencil {
     /// Apply function parameters to finalize a stencil into its final form.
     pub fn apply_params(self, params: &FunctionParameters) -> CompiledCode {
         CompiledCode {
-            buffer: self.buffer.apply_params(params),
+            buffer: self.buffer.apply_base_srcloc(params.base_srcloc()),
             frame_size: self.frame_size,
             disasm: self.disasm,
             value_labels_ranges: self.value_labels_ranges,