Auto merge of #98393 - michaelwoerister:new-cpp-like-enum-debuginfo, r=wesleywiser

debuginfo: Generalize C++-like encoding for enums.

The updated encoding should be able to handle niche layouts where more than one variant has fields (as introduced in https://github.com/rust-lang/rust/pull/94075).

The new encoding is more uniform as there is no structural difference between direct-tag, niche-tag, and no-tag layouts anymore. The only difference between those cases is that the "dataful" variant in a niche-tag enum will have a `(start, end)` pair denoting the tag range instead of a single value.

The new encoding now also supports 128-bit tags, which occur in at least some standard library types. These tags are represented as `u64` pairs so that debuggers (which don't always have support for 128-bit integers) can reliably deal with them. The downside is that this adds quite a bit of complexity to the encoding and especially to the corresponding NatVis.

The new encoding seems to increase the size of (x86_64-pc-windows-msvc) debuginfo by 10-15%. The size of binaries is not affected (release builds were built with `-Cdebuginfo=2`, numbers are in kilobytes):

EXE | before | after | relative
-- | -- | -- | --
cargo (debug) | 40453 | 40450 | +0%
ripgrep (debug) | 10275 | 10273 | +0%
cargo (release) | 16186 | 16185 | +0%
ripgrep (release) | 4727 | 4726 | +0%

PDB | before | after | relative
-- | -- | -- | --
cargo (debug) | 236524 | 261412 | +11%
ripgrep (debug) | 53140 | 59060 | +11%
cargo (release) | 148516 | 169620 | +14%
ripgrep (release) | 10676 | 11804 | +11%

Given that the new encoding is more general, this is to be expected. Only platforms using C++-like debuginfo are affected -- which currently is only `*-pc-windows-msvc`.

*TODO*
- [x] Properly update documentation
- [x] Add regression tests for new optimized enum layouts as introduced by #94075.

r? `@wesleywiser`

4 files changed, 12 insertions, 9 deletions

diff --git a/src/test/codegen/async-fn-debug-awaitee-field.rs b/src/test/codegen/async-fn-debug-awaitee-field.rs
index efb345fa9f3..909cd0062a6 100644
--- a/src/test/codegen/async-fn-debug-awaitee-field.rs
+++ b/src/test/codegen/async-fn-debug-awaitee-field.rs
@@ -12,11 +12,11 @@ async fn async_fn_test() {
 }
 
 // NONMSVC: [[GEN:!.*]] = !DICompositeType(tag: DW_TAG_structure_type, name: "{async_fn_env#0}",
-// MSVC: [[GEN:!.*]] = !DICompositeType(tag: DW_TAG_union_type, name: "enum$<async_fn_debug_awaitee_field::async_fn_test::async_fn_env$0>",
+// MSVC: [[GEN:!.*]] = !DICompositeType(tag: DW_TAG_union_type, name: "enum2$<async_fn_debug_awaitee_field::async_fn_test::async_fn_env$0>",
 // CHECK: [[SUSPEND_STRUCT:!.*]] = !DICompositeType(tag: DW_TAG_structure_type, name: "Suspend0", scope: [[GEN]],
 // CHECK: !DIDerivedType(tag: DW_TAG_member, name: "__awaitee", scope: [[SUSPEND_STRUCT]], {{.*}}, baseType: [[AWAITEE_TYPE:![0-9]*]],
 // NONMSVC: [[AWAITEE_TYPE]] = !DICompositeType(tag: DW_TAG_structure_type, name: "GenFuture<async_fn_debug_awaitee_field::foo::{async_fn_env#0}>",
-// MSVC: [[AWAITEE_TYPE]] = !DICompositeType(tag: DW_TAG_structure_type, name: "GenFuture<enum$<async_fn_debug_awaitee_field::foo::async_fn_env$0> >",
+// MSVC: [[AWAITEE_TYPE]] = !DICompositeType(tag: DW_TAG_structure_type, name: "GenFuture<enum2$<async_fn_debug_awaitee_field::foo::async_fn_env$0> >",
 
 fn main() {
     let _fn = async_fn_test();
diff --git a/src/test/codegen/async-fn-debug-msvc.rs b/src/test/codegen/async-fn-debug-msvc.rs
index 8995605e3dd..73c652c9dd1 100644
--- a/src/test/codegen/async-fn-debug-msvc.rs
+++ b/src/test/codegen/async-fn-debug-msvc.rs
@@ -16,7 +16,7 @@ async fn async_fn_test() {
 
 // FIXME: No way to reliably check the filename.
 
-// CHECK-DAG:  [[GEN:!.*]] = !DICompositeType(tag: DW_TAG_union_type, name: "enum$<async_fn_debug_msvc::async_fn_test::async_fn_env$0>",
+// CHECK-DAG:  [[GEN:!.*]] = !DICompositeType(tag: DW_TAG_union_type, name: "enum2$<async_fn_debug_msvc::async_fn_test::async_fn_env$0>",
 // CHECK:      {{!.*}} = !DIDerivedType(tag: DW_TAG_member, name: "variant0", scope: [[GEN]],
 // For brevity, we only check the struct name and members of the last variant.
 // CHECK-SAME: file: [[FILE:![0-9]*]], line: 11,
@@ -36,16 +36,17 @@ async fn async_fn_test() {
 // CHECK-SAME: )
 // CHECK:      {{!.*}} = !DIDerivedType(tag: DW_TAG_member, name: "variant4", scope: [[GEN]],
 // CHECK-SAME: file: [[FILE]], line: 14,
-// CHECK-SAME: baseType: [[VARIANT:![0-9]*]]
+// CHECK-SAME: baseType: [[VARIANT_WRAPPER:![0-9]*]]
 // CHECK-NOT:  flags: DIFlagArtificial
 // CHECK-SAME: )
+// CHECK:      {{!.*}} = !DIDerivedType(tag: DW_TAG_member, name: "value", scope: [[VARIANT_WRAPPER]], file: !2, baseType: [[VARIANT:![0-9]*]],
 // CHECK:      [[VARIANT]] = !DICompositeType(tag: DW_TAG_structure_type, name: "Suspend1", scope: [[GEN]],
 // CHECK-NOT:  flags: DIFlagArtificial
 // CHECK-SAME: )
 // CHECK:      {{!.*}} = !DIDerivedType(tag: DW_TAG_member, name: "s", scope: [[VARIANT]]
 // CHECK-NOT:  flags: DIFlagArtificial
 // CHECK-SAME: )
-// CHECK:      {{!.*}} = !DIDerivedType(tag: DW_TAG_member, name: "discriminant", scope: [[GEN]],
+// CHECK:      {{!.*}} = !DIDerivedType(tag: DW_TAG_member, name: "tag", scope: [[GEN]],
 // CHECK-NOT: flags: DIFlagArtificial
 
 fn main() {
diff --git a/src/test/codegen/debug-vtable.rs b/src/test/codegen/debug-vtable.rs
index b9cb4f93d07..bdd312878ec 100644
--- a/src/test/codegen/debug-vtable.rs
+++ b/src/test/codegen/debug-vtable.rs
@@ -46,7 +46,7 @@
 // CHECK: !DIDerivedType(tag: DW_TAG_member, name: "align", scope: ![[VTABLE_TY2]], {{.*}}, baseType: ![[USIZE]], size: {{64|32}}, align: {{64|32}}, offset: {{128|64}})
 
 // NONMSVC: !DIGlobalVariable(name: "<debug_vtable::bar::{closure_env#0} as core::ops::function::FnOnce<(core::option::Option<&dyn core::ops::function::Fn<(), Output=()>>)>>::{vtable}"
-// MSVC: !DIGlobalVariable(name: "impl$<debug_vtable::bar::closure_env$0, core::ops::function::FnOnce<tuple$<enum$<core::option::Option<ref$<dyn$<core::ops::function::Fn<tuple$<>,assoc$<Output,tuple$<> > > > > >, {{.*}}, {{.*}}, Some> > > >::vtable$"
+// MSVC: !DIGlobalVariable(name: "impl$<debug_vtable::bar::closure_env$0, core::ops::function::FnOnce<tuple$<enum2$<core::option::Option<ref$<dyn$<core::ops::function::Fn<tuple$<>,assoc$<Output,tuple$<> > > > > > > > > >::vtable$"
 
 // NONMSVC: !DIGlobalVariable(name: "<debug_vtable::generic_closure::{closure_env#0}<bool> as core::ops::function::FnOnce<()>>::{vtable}"
 // MSVC: !DIGlobalVariable(name: "impl$<debug_vtable::generic_closure::closure_env$0<bool>, core::ops::function::FnOnce<tuple$<> > >::vtable$
diff --git a/src/test/codegen/generator-debug-msvc.rs b/src/test/codegen/generator-debug-msvc.rs
index 033da80be16..b712068bf27 100644
--- a/src/test/codegen/generator-debug-msvc.rs
+++ b/src/test/codegen/generator-debug-msvc.rs
@@ -20,7 +20,7 @@ fn generator_test() -> impl Generator<Yield = i32, Return = ()> {
 
 // FIXME: No way to reliably check the filename.
 
-// CHECK-DAG:  [[GEN:!.*]] = !DICompositeType(tag: DW_TAG_union_type, name: "enum$<generator_debug_msvc::generator_test::generator_env$0>"
+// CHECK-DAG:  [[GEN:!.*]] = !DICompositeType(tag: DW_TAG_union_type, name: "enum2$<generator_debug_msvc::generator_test::generator_env$0>"
 // CHECK:      {{!.*}} = !DIDerivedType(tag: DW_TAG_member, name: "variant0", scope: [[GEN]],
 // For brevity, we only check the struct name and members of the last variant.
 // CHECK-SAME: file: [[FILE:![0-9]*]], line: 14,
@@ -40,16 +40,18 @@ fn generator_test() -> impl Generator<Yield = i32, Return = ()> {
 // CHECK-SAME: )
 // CHECK:      {{!.*}} = !DIDerivedType(tag: DW_TAG_member, name: "variant4", scope: [[GEN]],
 // CHECK-SAME: file: [[FILE]], line: 17,
-// CHECK-SAME: baseType: [[VARIANT:![0-9]*]]
+// CHECK-SAME: baseType: [[VARIANT_WRAPPER:![0-9]*]]
 // CHECK-NOT:  flags: DIFlagArtificial
 // CHECK-SAME: )
+// CHECK:      [[VARIANT_WRAPPER]] = !DICompositeType(tag: DW_TAG_structure_type, name: "Variant4", scope: [[GEN]],
+// CHECK:      !DIDerivedType(tag: DW_TAG_member, name: "value", scope: [[VARIANT_WRAPPER]], {{.*}}, baseType: [[VARIANT:![0-9]*]],
 // CHECK:      [[VARIANT]] = !DICompositeType(tag: DW_TAG_structure_type, name: "Suspend1", scope: [[GEN]],
 // CHECK-NOT:  flags: DIFlagArtificial
 // CHECK-SAME: )
 // CHECK:      {{!.*}} = !DIDerivedType(tag: DW_TAG_member, name: "s", scope: [[VARIANT]]
 // CHECK-NOT:  flags: DIFlagArtificial
 // CHECK-SAME: )
-// CHECK:      {{!.*}} = !DIDerivedType(tag: DW_TAG_member, name: "discriminant", scope: [[GEN]],
+// CHECK:      {{!.*}} = !DIDerivedType(tag: DW_TAG_member, name: "tag", scope: [[GEN]],
 // CHECK-NOT: flags: DIFlagArtificial
 
 fn main() {