Auto merge of #109808 - jyn514:debuginfo-options, r=michaelwoerister

Extend -Cdebuginfo with new options and named aliases

This is a rebase of #83947, along with my best guess at what the new options mean. I tried to follow the LLVM source code to get a better idea but ran into quite a lot of trouble (https://rust-lang.zulipchat.com/#narrow/stream/187780-t-compiler.2Fwg-llvm/topic/go-to-definition.20in.20src.2Fllvm-project.3F). The description for the original PR follows below.

Note that the changes in this PR have already been through FCP: #83947 (comment)

Closes #109311. Helps with #104968.
r? `@michaelwoerister` cc `@cuviper`

---

The -Cdebuginfo=1 option was never line tables only and can't be due to backwards compatibility issues. This was clarified and an option for emitting line tables only was added. Additionally an option for emitting line info directives only was added, which is needed for some targets, i.e. nvptx. The debug info options should now behave similarly to clang's debug info options.

Fix #60020
Fix #64405

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -830,24 +830,7 @@ pub fn build_compile_unit_di_node<'ll, 'tcx>(
     }
     .unwrap_or_default();
     let split_name = split_name.to_str().unwrap();
-
-    // FIXME(#60020):
-    //
-    //    This should actually be
-    //
-    //        let kind = DebugEmissionKind::from_generic(tcx.sess.opts.debuginfo);
-    //
-    //    That is, we should set LLVM's emission kind to `LineTablesOnly` if
-    //    we are compiling with "limited" debuginfo. However, some of the
-    //    existing tools relied on slightly more debuginfo being generated than
-    //    would be the case with `LineTablesOnly`, and we did not want to break
-    //    these tools in a "drive-by fix", without a good idea or plan about
-    //    what limited debuginfo should exactly look like. So for now we keep
-    //    the emission kind as `FullDebug`.
-    //
-    //    See https://github.com/rust-lang/rust/issues/60020 for details.
-    let kind = DebugEmissionKind::FullDebug;
-    assert!(tcx.sess.opts.debuginfo != DebugInfo::None);
+    let kind = DebugEmissionKind::from_generic(tcx.sess.opts.debuginfo);
 
     unsafe {
         let compile_unit_file = llvm::LLVMRustDIBuilderCreateFile(

compiler/rustc_codegen_llvm/src/debuginfo/mod.rs

@@ -402,7 +402,7 @@ impl<'ll, 'tcx> DebugInfoMethods<'tcx> for CodegenCx<'ll, 'tcx> {
             cx: &CodegenCx<'ll, 'tcx>,
             fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
         ) -> &'ll DIArray {
-            if cx.sess().opts.debuginfo == DebugInfo::Limited {
+            if cx.sess().opts.debuginfo != DebugInfo::Full {
                 return create_DIArray(DIB(cx), &[]);
             }
 

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -946,15 +946,27 @@ pub mod debuginfo {
         NoDebug,
         FullDebug,
         LineTablesOnly,
+        DebugDirectivesOnly,
     }
 
     impl DebugEmissionKind {
         pub fn from_generic(kind: rustc_session::config::DebugInfo) -> Self {
+            // We should be setting LLVM's emission kind to `LineTablesOnly` if
+            // we are compiling with "limited" debuginfo. However, some of the
+            // existing tools relied on slightly more debuginfo being generated than
+            // would be the case with `LineTablesOnly`, and we did not want to break
+            // these tools in a "drive-by fix", without a good idea or plan about
+            // what limited debuginfo should exactly look like. So for now we are
+            // instead adding a new debuginfo option "line-tables-only" so as to
+            // not break anything and to allow users to have 'limited' debug info.
+            //
+            // See https://github.com/rust-lang/rust/issues/60020 for details.
             use rustc_session::config::DebugInfo;
             match kind {
                 DebugInfo::None => DebugEmissionKind::NoDebug,
-                DebugInfo::Limited => DebugEmissionKind::LineTablesOnly,
-                DebugInfo::Full => DebugEmissionKind::FullDebug,
+                DebugInfo::LineDirectivesOnly => DebugEmissionKind::DebugDirectivesOnly,
+                DebugInfo::LineTablesOnly => DebugEmissionKind::LineTablesOnly,
+                DebugInfo::Limited | DebugInfo::Full => DebugEmissionKind::FullDebug,
             }
         }
     }

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -1121,9 +1121,12 @@ impl<'a> Linker for EmLinker<'a> {
 
     fn debuginfo(&mut self, _strip: Strip, _: &[PathBuf]) {
         // Preserve names or generate source maps depending on debug info
+        // For more information see https://emscripten.org/docs/tools_reference/emcc.html#emcc-g
         self.cmd.arg(match self.sess.opts.debuginfo {
             DebugInfo::None => "-g0",
-            DebugInfo::Limited => "--profiling-funcs",
+            DebugInfo::Limited | DebugInfo::LineTablesOnly | DebugInfo::LineDirectivesOnly => {
+                "--profiling-funcs"
+            }
             DebugInfo::Full => "-g",
         });
     }

compiler/rustc_interface/src/tests.rs

@@ -5,6 +5,7 @@ use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::profiling::TimePassesFormat;
 use rustc_errors::{emitter::HumanReadableErrorType, registry, ColorConfig};
 use rustc_session::config::rustc_optgroups;
+use rustc_session::config::DebugInfo;
 use rustc_session::config::Input;
 use rustc_session::config::InstrumentXRay;
 use rustc_session::config::TraitSolver;
@@ -574,7 +575,7 @@ fn test_codegen_options_tracking_hash() {
     tracked!(code_model, Some(CodeModel::Large));
     tracked!(control_flow_guard, CFGuard::Checks);
     tracked!(debug_assertions, Some(true));
-    tracked!(debuginfo, 0xdeadbeef);
+    tracked!(debuginfo, DebugInfo::Limited);
     tracked!(embed_bitcode, false);
     tracked!(force_frame_pointers, Some(false));
     tracked!(force_unwind_tables, Some(true));

compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -682,6 +682,7 @@ enum class LLVMRustDebugEmissionKind {
   NoDebug,
   FullDebug,
   LineTablesOnly,
+  DebugDirectivesOnly,
 };
 
 static DICompileUnit::DebugEmissionKind fromRust(LLVMRustDebugEmissionKind Kind) {
@@ -692,6 +693,8 @@ static DICompileUnit::DebugEmissionKind fromRust(LLVMRustDebugEmissionKind Kind)
     return DICompileUnit::DebugEmissionKind::FullDebug;
   case LLVMRustDebugEmissionKind::LineTablesOnly:
     return DICompileUnit::DebugEmissionKind::LineTablesOnly;
+  case LLVMRustDebugEmissionKind::DebugDirectivesOnly:
+    return DICompileUnit::DebugEmissionKind::DebugDirectivesOnly;
   default:
     report_fatal_error("bad DebugEmissionKind.");
   }

compiler/rustc_session/src/config.rs

@@ -260,6 +260,8 @@ pub enum SymbolManglingVersion {
 #[derive(Clone, Copy, Debug, PartialEq, Hash)]
 pub enum DebugInfo {
     None,
+    LineDirectivesOnly,
+    LineTablesOnly,
     Limited,
     Full,
 }
@@ -1979,11 +1981,7 @@ fn parse_opt_level(
     }
 }
 
-fn select_debuginfo(
-    matches: &getopts::Matches,
-    cg: &CodegenOptions,
-    error_format: ErrorOutputType,
-) -> DebugInfo {
+fn select_debuginfo(matches: &getopts::Matches, cg: &CodegenOptions) -> DebugInfo {
     let max_g = matches.opt_positions("g").into_iter().max();
     let max_c = matches
         .opt_strs_pos("C")
@@ -1993,24 +1991,7 @@ fn select_debuginfo(
             if let Some("debuginfo") = s.split('=').next() { Some(i) } else { None }
         })
         .max();
-    if max_g > max_c {
-        DebugInfo::Full
-    } else {
-        match cg.debuginfo {
-            0 => DebugInfo::None,
-            1 => DebugInfo::Limited,
-            2 => DebugInfo::Full,
-            arg => {
-                early_error(
-                    error_format,
-                    &format!(
-                        "debug info level needs to be between \
-                         0-2 (instead was `{arg}`)"
-                    ),
-                );
-            }
-        }
-    }
+    if max_g > max_c { DebugInfo::Full } else { cg.debuginfo }
 }
 
 pub(crate) fn parse_assert_incr_state(
@@ -2498,7 +2479,7 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
     // to use them interchangeably. See the note above (regarding `-O` and `-C opt-level`)
     // for more details.
     let debug_assertions = cg.debug_assertions.unwrap_or(opt_level == OptLevel::No);
-    let debuginfo = select_debuginfo(matches, &cg, error_format);
+    let debuginfo = select_debuginfo(matches, &cg);
 
     let mut search_paths = vec![];
     for s in &matches.opt_strs("L") {

compiler/rustc_session/src/options.rs

@@ -377,6 +377,7 @@ mod desc {
     pub const parse_cfguard: &str =
         "either a boolean (`yes`, `no`, `on`, `off`, etc), `checks`, or `nochecks`";
     pub const parse_cfprotection: &str = "`none`|`no`|`n` (default), `branch`, `return`, or `full`|`yes`|`y` (equivalent to `branch` and `return`)";
+    pub const parse_debuginfo: &str = "either an integer (0, 1, 2), `none`, `line-directives-only`, `line-tables-only`, `limited`, or `full`";
     pub const parse_strip: &str = "either `none`, `debuginfo`, or `symbols`";
     pub const parse_linker_flavor: &str = ::rustc_target::spec::LinkerFlavorCli::one_of();
     pub const parse_optimization_fuel: &str = "crate=integer";
@@ -767,6 +768,18 @@ mod parse {
         true
     }
 
+    pub(crate) fn parse_debuginfo(slot: &mut DebugInfo, v: Option<&str>) -> bool {
+        match v {
+            Some("0") | Some("none") => *slot = DebugInfo::None,
+            Some("line-directives-only") => *slot = DebugInfo::LineDirectivesOnly,
+            Some("line-tables-only") => *slot = DebugInfo::LineTablesOnly,
+            Some("1") | Some("limited") => *slot = DebugInfo::Limited,
+            Some("2") | Some("full") => *slot = DebugInfo::Full,
+            _ => return false,
+        }
+        true
+    }
+
     pub(crate) fn parse_linker_flavor(slot: &mut Option<LinkerFlavorCli>, v: Option<&str>) -> bool {
         match v.and_then(LinkerFlavorCli::from_str) {
             Some(lf) => *slot = Some(lf),
@@ -1217,9 +1230,9 @@ options! {
         "use Windows Control Flow Guard (default: no)"),
     debug_assertions: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "explicitly enable the `cfg(debug_assertions)` directive"),
-    debuginfo: usize = (0, parse_number, [TRACKED],
-        "debug info emission level (0 = no debug info, 1 = line tables only, \
-        2 = full debug info with variable and type information; default: 0)"),
+    debuginfo: DebugInfo = (DebugInfo::None, parse_debuginfo, [TRACKED],
+        "debug info emission level (0-2, none, line-directives-only, \
+        line-tables-only, limited, or full; default: 0)"),
     default_linker_libraries: bool = (false, parse_bool, [UNTRACKED],
         "allow the linker to link its default libraries (default: no)"),
     embed_bitcode: bool = (true, parse_bool, [TRACKED],

src/doc/rustc/src/codegen-options/index.md

@@ -71,9 +71,11 @@ If not specified, debug assertions are automatically enabled only if the
 This flag controls the generation of debug information. It takes one of the
 following values:
 
-* `0`: no debug info at all (the default).
-* `1`: line tables only.
-* `2`: full debug info.
+* `0` or `none`: no debug info at all (the default).
+* `line-directives-only`: line info directives only. For the nvptx* targets this enables [profiling](https://reviews.llvm.org/D46061). For other use cases, `line-tables-only` is the better, more compatible choice.
+* `line-tables-only`: line tables only. Generates the minimal amount of debug info for backtraces with filename/line number info, but not anything else, i.e. no variable or function parameter info.
+* `1` or `limited`: debug info without type or variable-level information.
+* `2` or `full`: full debug info.
 
 Note: The [`-g` flag][option-g-debug] is an alias for `-C debuginfo=2`.
 

tests/codegen/debug-limited.rs

@@ -0,0 +1,27 @@
+// Verify that the limited debuginfo option emits llvm's FullDebugInfo, but no type info.
+//
+// compile-flags: -C debuginfo=limited
+
+#[repr(C)]
+struct StructType {
+    a: i64,
+    b: i32,
+}
+
+extern "C" {
+    fn creator() -> *mut StructType;
+    fn save(p: *const StructType);
+}
+
+fn main() {
+    unsafe {
+        let value: &mut StructType = &mut *creator();
+        value.a = 7;
+        save(value as *const StructType)
+    }
+}
+
+// CHECK: !DICompileUnit
+// CHECK: emissionKind: FullDebug
+// CHECK: !DILocation
+// CHECK-NOT: !DIBasicType

tests/codegen/debug-line-directives-only.rs

@@ -0,0 +1,27 @@
+// Verify that the only debuginfo generated are the line directives.
+//
+// compile-flags: -C debuginfo=line-directives-only
+
+#[repr(C)]
+struct StructType {
+    a: i64,
+    b: i32,
+}
+
+extern "C" {
+    fn creator() -> *mut StructType;
+    fn save(p: *const StructType);
+}
+
+fn main() {
+    unsafe {
+        let value: &mut StructType = &mut *creator();
+        value.a = 7;
+        save(value as *const StructType)
+    }
+}
+
+// CHECK: !DICompileUnit
+// CHECK: emissionKind: DebugDirectivesOnly
+// CHECK: !DILocation
+// CHECK-NOT: !DIBasicType

tests/codegen/debug-line-tables-only.rs

@@ -0,0 +1,27 @@
+// Verify that the only debuginfo generated are the line tables.
+//
+// compile-flags: -C debuginfo=line-tables-only
+
+#[repr(C)]
+struct StructType {
+    a: i64,
+    b: i32,
+}
+
+extern "C" {
+    fn creator() -> *mut StructType;
+    fn save(p: *const StructType);
+}
+
+fn main() {
+    unsafe {
+        let value: &mut StructType = &mut *creator();
+        value.a = 7;
+        save(value as *const StructType)
+    }
+}
+
+// CHECK: !DICompileUnit
+// CHECK: emissionKind: LineTablesOnly
+// CHECK: !DILocation
+// CHECK-NOT: !DIBasicType

tests/rustdoc-ui/c-help.stdout

@@ -3,7 +3,7 @@
     -C            codegen-units=val -- divide crate into N units to optimize in parallel
     -C       control-flow-guard=val -- use Windows Control Flow Guard (default: no)
     -C         debug-assertions=val -- explicitly enable the `cfg(debug_assertions)` directive
-    -C                debuginfo=val -- debug info emission level (0 = no debug info, 1 = line tables only, 2 = full debug info with variable and type information; default: 0)
+    -C                debuginfo=val -- debug info emission level (0-2, none, line-directives-only, line-tables-only, limited, or full; default: 0)
     -C default-linker-libraries=val -- allow the linker to link its default libraries (default: no)
     -C            embed-bitcode=val -- emit bitcode in rlibs (default: yes)
     -C           extra-filename=val -- extra data to put in each output filename