Add debugPrintf-based panic reporting, controlled via spirv_builder::ShaderPanicStrategy.

Author: eddyb

CHANGELOG.md

@@ -29,6 +29,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added ⭐
+- [PR#1080](https://github.com/EmbarkStudios/rust-gpu/pull/1080) added `debugPrintf`-based
+  panic reporting, with the desired behavior selected via `spirv_builder::ShaderPanicStrategy`
+  (see its documentation for more details about each available panic handling strategy)
+
 ### Changed 🛠
 - [PR#1079](https://github.com/EmbarkStudios/rust-gpu/pull/1079) revised `spirv-builder`'s `README.md`,
   and added a way for `docs.rs` to be able to build it (via `cargo +stable doc --no-default-features`)

crates/rustc_codegen_spirv/src/builder/builder_methods.rs

@@ -13,7 +13,7 @@ use rustc_codegen_ssa::common::{
 use rustc_codegen_ssa::mir::operand::{OperandRef, OperandValue};
 use rustc_codegen_ssa::mir::place::PlaceRef;
 use rustc_codegen_ssa::traits::{
-    BackendTypes, BuilderMethods, ConstMethods, IntrinsicCallMethods, LayoutTypeMethods, OverflowOp,
+    BackendTypes, BuilderMethods, ConstMethods, LayoutTypeMethods, OverflowOp,
 };
 use rustc_codegen_ssa::MemFlags;
 use rustc_data_structures::fx::FxHashSet;
@@ -2647,7 +2647,8 @@ impl<'a, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'tcx> {
 
             // HACK(eddyb) redirect any possible panic call to an abort, to avoid
             // needing to materialize `&core::panic::Location` or `format_args!`.
-            self.abort();
+            // FIXME(eddyb) find a way to extract the original message.
+            self.abort_with_message("panic!(...)".into());
             self.undef(result_type)
         } else if let Some(mode) = buffer_load_intrinsic {
             self.codegen_buffer_load_intrinsic(result_type, args, mode)

crates/rustc_codegen_spirv/src/builder/intrinsics.rs

@@ -4,6 +4,7 @@ use crate::builder_spirv::{SpirvValue, SpirvValueExt};
 use crate::codegen_cx::CodegenCx;
 use crate::custom_insts::CustomInst;
 use crate::spirv_type::SpirvType;
+use rspirv::dr::Operand;
 use rspirv::spirv::GLOp;
 use rustc_codegen_ssa::mir::operand::OperandRef;
 use rustc_codegen_ssa::mir::place::PlaceRef;
@@ -338,18 +339,7 @@ impl<'a, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'a, 'tcx> {
     }
 
     fn abort(&mut self) {
-        // FIXME(eddyb) this should be cached more efficiently.
-        let void_ty = SpirvType::Void.def(rustc_span::DUMMY_SP, self);
-
-        // HACK(eddyb) there is no `abort` or `trap` instruction in SPIR-V,
-        // so the best thing we can do is use our own custom instruction.
-        self.custom_inst(void_ty, CustomInst::Abort);
-        self.unreachable();
-
-        // HACK(eddyb) we still need an active block in case the user of this
-        // `Builder` will continue to emit instructions after the `.abort()`.
-        let post_abort_dead_bb = self.append_sibling_block("post_abort_dead");
-        self.switch_to_block(post_abort_dead_bb);
+        self.abort_with_message("intrinsics::abort()".into());
     }
 
     fn assume(&mut self, _val: Self::Value) {
@@ -382,3 +372,26 @@ impl<'a, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'a, 'tcx> {
         todo!()
     }
 }
+
+impl Builder<'_, '_> {
+    pub fn abort_with_message(&mut self, message: String) {
+        // FIXME(eddyb) this should be cached more efficiently.
+        let void_ty = SpirvType::Void.def(rustc_span::DUMMY_SP, self);
+
+        // HACK(eddyb) there is no `abort` or `trap` instruction in SPIR-V,
+        // so the best thing we can do is use our own custom instruction.
+        let message_id = self.emit().string(message);
+        self.custom_inst(
+            void_ty,
+            CustomInst::Abort {
+                message: Operand::IdRef(message_id),
+            },
+        );
+        self.unreachable();
+
+        // HACK(eddyb) we still need an active block in case the user of this
+        // `Builder` will continue to emit instructions after the `.abort()`.
+        let post_abort_dead_bb = self.append_sibling_block("post_abort_dead");
+        self.switch_to_block(post_abort_dead_bb);
+    }
+}

crates/rustc_codegen_spirv/src/codegen_cx/mod.rs

@@ -348,6 +348,12 @@ impl CodegenArgs {
                 "enable additional SPIR-T passes (comma-separated)",
                 "PASSES",
             );
+            opts.optopt(
+                "",
+                "abort-strategy",
+                "select a non-default abort (i.e. panic) strategy - see `spirv-builder` docs",
+                "STRATEGY",
+            );
 
             // NOTE(eddyb) these are debugging options that used to be env vars
             // (for more information see `docs/src/codegen-args.md`).
@@ -529,6 +535,8 @@ impl CodegenArgs {
                 .map(|s| s.to_string())
                 .collect(),
 
+            abort_strategy: matches.opt_str("abort-strategy"),
+
             // FIXME(eddyb) deduplicate between `CodegenArgs` and `linker::Options`.
             emit_multiple_modules: module_output_type == ModuleOutputType::Multiple,
             spirv_metadata,

crates/rustc_codegen_spirv/src/custom_insts.rs

@@ -138,15 +138,15 @@ def_custom_insts! {
     // an additional returned `bool`, instead (i.e. a form of emulated unwinding).
     //
     // As this is a custom terminator, it must only appear before `OpUnreachable`,
-    // *without* any instructions in between (not even debuginfo ones).
+    // with at most debuginfo instructions (standard or custom), between the two.
     //
     // FIXME(eddyb) long-term this kind of custom control-flow could be generalized
     // to fully emulate unwinding (resulting in codegen similar to `?` in functions
     // returning `Option` or `Result`), to e.g. run destructors, or even allow
     // users to do `catch_unwind` at the top-level of their shader to handle
     // panics specially (e.g. by appending to a custom buffer, or using some
     // specific color in a fragment shader, to indicate a panic happened).
-    4 => Abort,
+    4 => Abort { message },
 }
 
 impl CustomOp {
@@ -164,8 +164,8 @@ impl CustomOp {
     }
 
     /// Returns `true` iff this `CustomOp` is a custom terminator instruction,
-    /// i.e. semantic and must always appear just before an `OpUnreachable`
-    /// standard terminator (without even debuginfo in between the two).
+    /// i.e. semantic and must precede an `OpUnreachable` standard terminator,
+    /// with at most debuginfo instructions (standard or custom), between the two.
     pub fn is_terminator(self) -> bool {
         match self {
             CustomOp::SetDebugSrcLoc