Improve error messages received from Cranelift (#583)

As discussed in https://github.com/bytecodealliance/cranelift/pull/1226, the context of Cranelift errors is lost after exiting the scope containing the Cranelift function. `CodegenError` then only contains something like `inst2: arg 0 (v4) has type i16x8, expected i8x16`, which is rarely enough information for investigating a codegen failure. This change uses Cranelift's `pretty_error` function to improve the error messages wrapped in `CompileError`; `CompileError` has lost the reference to `CodegenError` due to `pretty_error` taking ownership but this seems preferable since no backtrace is attached and losing the pretty-printed context would be worse (if `CodegenError` gains a `Backtrace` or implements `Clone` we can revisit this).

crates/api/src/trampoline/func.rs

@@ -7,6 +7,7 @@ use alloc::{boxed::Box, rc::Rc, string::ToString, vec::Vec};
 use anyhow::Result;
 use core::cmp;
 use cranelift_codegen::ir::{types, InstBuilder, StackSlotData, StackSlotKind, TrapCode};
+use cranelift_codegen::print_errors::pretty_error;
 use cranelift_codegen::{binemit, ir, isa, Context};
 use cranelift_entity::{EntityRef, PrimaryMap};
 use cranelift_frontend::{FunctionBuilder, FunctionBuilderContext};
@@ -174,6 +175,7 @@ fn make_trampoline(
             &mut trap_sink,
             &mut stackmap_sink,
         )
+        .map_err(|error| pretty_error(&context.func, Some(isa), error))
         .expect("compile_and_emit");
 
     let mut unwind_info = Vec::new();

crates/environ/src/compilation.rs

@@ -5,7 +5,7 @@ use crate::address_map::{ModuleAddressMap, ValueLabelsRanges};
 use crate::module;
 use crate::module_environ::FunctionBodyData;
 use alloc::vec::Vec;
-use cranelift_codegen::{binemit, ir, isa, CodegenError};
+use cranelift_codegen::{binemit, ir, isa};
 use cranelift_entity::PrimaryMap;
 use cranelift_wasm::{DefinedFuncIndex, FuncIndex, ModuleTranslationState, WasmError};
 use serde::{Deserialize, Serialize};
@@ -156,8 +156,8 @@ pub enum CompileError {
     Wasm(#[from] WasmError),
 
     /// A compilation error occured.
-    #[error("Compilation error")]
-    Codegen(#[from] CodegenError),
+    #[error("Compilation error: {0}")]
+    Codegen(String),
 
     /// A compilation error occured.
     #[error("Debug info is not supported with this configuration")]

crates/environ/src/cranelift.rs

@@ -19,6 +19,7 @@ use cranelift_codegen::binemit;
 use cranelift_codegen::ir;
 use cranelift_codegen::ir::ExternalName;
 use cranelift_codegen::isa;
+use cranelift_codegen::print_errors::pretty_error;
 use cranelift_codegen::Context;
 use cranelift_entity::PrimaryMap;
 use cranelift_wasm::{DefinedFuncIndex, FuncIndex, FuncTranslator, ModuleTranslationState};
@@ -239,13 +240,21 @@ impl crate::compilation::Compiler for Cranelift {
                             let mut reloc_sink = RelocSink::new(func_index);
                             let mut trap_sink = TrapSink::new();
                             let mut stackmap_sink = binemit::NullStackmapSink {};
-                            context.compile_and_emit(
+                            context
+                                .compile_and_emit(
                                     isa,
                                     &mut code_buf,
                                     &mut reloc_sink,
                                     &mut trap_sink,
                                     &mut stackmap_sink,
-                            )?;
+                                )
+                                .map_err(|error| {
+                                    CompileError::Codegen(pretty_error(
+                                        &context.func,
+                                        Some(isa),
+                                        error,
+                                    ))
+                                })?;
 
                             context.emit_unwind_info(isa, &mut unwind_info);
 
@@ -257,7 +266,15 @@ impl crate::compilation::Compiler for Cranelift {
                             };
 
                             let ranges = if generate_debug_info {
-                                Some(context.build_value_labels_ranges(isa)?)
+                                let ranges =
+                                    context.build_value_labels_ranges(isa).map_err(|error| {
+                                        CompileError::Codegen(pretty_error(
+                                            &context.func,
+                                            Some(isa),
+                                            error,
+                                        ))
+                                    })?;
+                                Some(ranges)
                             } else {
                                 None
                             };

crates/jit/src/compiler.rs

@@ -10,6 +10,7 @@ use alloc::vec::Vec;
 use core::convert::TryFrom;
 use cranelift_codegen::ir::InstBuilder;
 use cranelift_codegen::isa::{TargetFrontendConfig, TargetIsa};
+use cranelift_codegen::print_errors::pretty_error;
 use cranelift_codegen::Context;
 use cranelift_codegen::{binemit, ir};
 use cranelift_entity::{EntityRef, PrimaryMap};
@@ -336,7 +337,13 @@ fn make_trampoline(
             &mut trap_sink,
             &mut stackmap_sink,
         )
-        .map_err(|error| SetupError::Compile(CompileError::Codegen(error)))?;
+        .map_err(|error| {
+            SetupError::Compile(CompileError::Codegen(pretty_error(
+                &context.func,
+                Some(isa),
+                error,
+            )))
+        })?;
 
     context.emit_unwind_info(isa, &mut unwind_info);