Add custom_insts for our own OpExtInsts, and use it for some debuginfo.

[eddyb]

This PR introduces a Rust-GPU-specific custom "extended instruction set" (OpExtInstImport/OpExtInst - note that unlike the requirements imposed by the SPIR-V specification, we're only concerned about rspirv/spirt compatibility, as long as we always rewrite such instructions before the final SPIR-V output).

Longer-term, we'll likely want such custom instructions for more advanced usecases (e.g. one idea being floated around was adding our own OpAbort that gets transformed to standard SPIR-V), and the debuginfo needs will likely get superseded by adopting NonSemantic.Shader.DebugInfo.100, but for now this is easier for some debuginfo.

The main feature this PR adds is the ability to have location ranges, not just the starting point:

before this PR (since #1040)

after this PR

error: cannot memcpy dynamically sized data --> $CORE_SRC/intrinsics.rs:2460:9 | 2460 | copy(src, dst, count) | ^ | note: used from within `core::intrinsics::copy::` --> $CORE_SRC/intrinsics.rs:2447:21 | 2447 | pub const unsafe fn copy(src: *const T, dst: *mut T, count: usize) { | ^ note: called by `ptr_copy::copy_via_raw_ptr` --> $DIR/ptr_copy.rs:28:18 | 28 | unsafe { core::ptr::copy(src, dst, 1) } | ^ note: called by `ptr_copy::main` --> $DIR/ptr_copy.rs:33:5 | 33 | copy_via_raw_ptr(&i, o); | ^ note: called by `main` --> $DIR/ptr_copy.rs:31:1 | 31 | #[spirv(fragment)] | ^

error: cannot memcpy dynamically sized data --> $CORE_SRC/intrinsics.rs:2460:9 | 2460 | copy(src, dst, count) | ^^^^^^^^^^^^^^^^^^^^^ | note: used from within `core::intrinsics::copy::` --> $CORE_SRC/intrinsics.rs:2447:21 | 2447 | pub const unsafe fn copy(src: *const T, dst: *mut T, count: usize) { | ^^^^ note: called by `ptr_copy::copy_via_raw_ptr` --> $DIR/ptr_copy.rs:28:18 | 28 | unsafe { core::ptr::copy(src, dst, 1) } | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ note: called by `ptr_copy::main` --> $DIR/ptr_copy.rs:33:5 | 33 | copy_via_raw_ptr(&i, o); | ^^^^^^^^^^^^^^^^^^^^^^^ note: called by `main` --> $DIR/ptr_copy.rs:32:8 | 32 | pub fn main(i: f32, o: &mut f32) { | ^^^^

The other feature is inline stack frames, e.g. most of this --no-early-report-zombies output is new:
^{_{(actually, it used to not even report the zombies, because the decorations were being lost)}}

error: cannot memcpy dynamically sized data --> $CORE_SRC/intrinsics.rs:2460:9 | 2460 | copy(src, dst, count) | ^^^^^^^^^^^^^^^^^^^^^ | note: used from within `core::intrinsics::copy::` --> $CORE_SRC/intrinsics.rs:2460:9 | 2460 | copy(src, dst, count) | ^^^^^^^^^^^^^^^^^^^^^ note: called by `ptr_copy::copy_via_raw_ptr` --> $DIR/ptr_copy.rs:28:18 | 28 | unsafe { core::ptr::copy(src, dst, 1) } | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ note: called by `ptr_copy::main` --> $DIR/ptr_copy.rs:33:5 | 33 | copy_via_raw_ptr(&i, o); | ^^^^^^^^^^^^^^^^^^^^^^^ note: called by Fragment entry-point `main` --> $DIR/ptr_copy.rs:32:8 | 32 | pub fn main(i: f32, o: &mut f32) { | ^^^^ error: cannot memcpy dynamically sized data --> $CORE_SRC/intrinsics.rs:2460:9 | 2460 | copy(src, dst, count) | ^^^^^^^^^^^^^^^^^^^^^ | note: used from within `ptr_copy::copy_via_raw_ptr` --> $DIR/ptr_copy.rs:11:4 | 11 | fn copy_via_raw_ptr(src: &f32, dst: &mut f32) { | ^^^^^^^^^^^^^^^^ note: called by `ptr_copy::main` --> $DIR/ptr_copy.rs:38:5 | 38 | copy_via_raw_ptr(&src, &mut dst); | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ note: called by Fragment entry-point `main` --> $DIR/ptr_copy.rs:32:8 | 32 | pub fn main(i: f32, o: &mut f32) { | ^^^^

The more flexible debuginfo is only used internally, and replaced with standard SPIR-V OpLine/OpNoLine instructions (or rather, the SPIR-T attribute that spirt::spv::lift maps to OpLine/OpNoLine) after all possible (zombie or SPIR-T) diagnostics have been emitted, to maximize our diagnostics quality.

[VZout]

fancy!

also learned some new rust :p if let [Operand::IdRef(target), ..] = inst.operands[..] {