debuginfo: emit DW_TAG_call_site entries on optimized builds

compiler/rustc_codegen_llvm/src/debuginfo/mod.rs

@@ -483,6 +483,10 @@ impl<'ll, 'tcx> DebugInfoCodegenMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         }
         if self.sess().opts.optimize != config::OptLevel::No {
             spflags |= DISPFlags::SPFlagOptimized;
+            // Emit DW_TAG_call_site entries for optimized builds, matching
+            // Clang's behavior. At -O0 no tail-call optimization occurs, so
+            // the debugger can reconstruct the call stack without them.
+            flags |= DIFlags::FlagAllCallsDescribed;
         }
         if let Some((id, _)) = tcx.entry_fn(()) {
             if id == def_id {
@@ -494,6 +498,9 @@ impl<'ll, 'tcx> DebugInfoCodegenMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         // LLVM LTO can't unify type definitions when a child DIE is a full subprogram definition.
         // When we use this `decl` below, the subprogram definition gets created at the CU level
         // with a DW_AT_specification pointing back to the type's declaration.
+        // FlagAllCallsDescribed cannot appear on the method declaration DIE
+        // because it has no body, which LLVM's verifier rejects.
+        let decl_flags = flags & !DIFlags::FlagAllCallsDescribed;
         let decl = is_method.then(|| unsafe {
             llvm::LLVMRustDIBuilderCreateMethod(
                 DIB(self),
@@ -505,7 +512,7 @@ impl<'ll, 'tcx> DebugInfoCodegenMethods<'tcx> for CodegenCx<'ll, 'tcx> {
                 file_metadata,
                 loc.line,
                 function_type_metadata,
-                flags,
+                decl_flags,
                 spflags & !DISPFlags::SPFlagDefinition,
                 template_parameters,
             )

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -781,6 +781,7 @@ pub(crate) mod debuginfo {
             const FlagNonTrivial          = (1 << 26);
             const FlagBigEndian           = (1 << 27);
             const FlagLittleEndian        = (1 << 28);
+            const FlagAllCallsDescribed   = (1 << 29);
         }
     }
 

compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -779,6 +779,7 @@ ASSERT_DIFLAG_VALUE(FlagThunk, 1 << 25);
 ASSERT_DIFLAG_VALUE(FlagNonTrivial, 1 << 26);
 ASSERT_DIFLAG_VALUE(FlagBigEndian, 1 << 27);
 ASSERT_DIFLAG_VALUE(FlagLittleEndian, 1 << 28);
+static_assert(DINode::DIFlags::FlagAllCallsDescribed == (1 << 29));
 ASSERT_DIFLAG_VALUE(FlagIndirectVirtualBase, (1 << 2) | (1 << 5));
 #undef ASSERT_DIFLAG_VALUE
 
@@ -791,7 +792,7 @@ ASSERT_DIFLAG_VALUE(FlagIndirectVirtualBase, (1 << 2) | (1 << 5));
 // to copying each bit/subvalue.
 static DINode::DIFlags fromRust(LLVMDIFlags Flags) {
   // Check that all set bits are covered by the static assertions above.
-  const unsigned UNKNOWN_BITS = (1 << 31) | (1 << 30) | (1 << 29) | (1 << 21);
+  const unsigned UNKNOWN_BITS = (1 << 31) | (1 << 30) | (1 << 21);
   if (Flags & UNKNOWN_BITS) {
     report_fatal_error("bad LLVMDIFlags");
   }

tests/codegen-llvm/debuginfo-callsite-flag-noopt.rs

@@ -0,0 +1,23 @@
+// Check that DIFlagAllCallsDescribed is NOT set in unoptimized builds.
+// At -O0 no tail-call optimization occurs, so the debugger can
+// reconstruct the call stack without DW_TAG_call_site entries.
+
+//@ ignore-msvc (CodeView does not use DIFlagAllCallsDescribed)
+//@ compile-flags: -C debuginfo=2 -C opt-level=0 -C no-prepopulate-passes
+
+#![crate_type = "lib"]
+
+// CHECK: {{.*}}DISubprogram{{.*}}name: "foo"
+// CHECK-NOT: DIFlagAllCallsDescribed
+
+#[no_mangle]
+#[inline(never)]
+pub fn foo(x: i32) -> i32 {
+    bar(x + 1)
+}
+
+#[no_mangle]
+#[inline(never)]
+pub fn bar(x: i32) -> i32 {
+    x * 2
+}

tests/codegen-llvm/debuginfo-callsite-flag.rs

@@ -0,0 +1,21 @@
+// Check that DIFlagAllCallsDescribed is set on subprogram definitions
+// in optimized builds, so LLVM emits DW_TAG_call_site entries.
+
+//@ ignore-msvc (CodeView does not use DIFlagAllCallsDescribed)
+//@ compile-flags: -C debuginfo=2 -C opt-level=1 -C no-prepopulate-passes
+
+#![crate_type = "lib"]
+
+// CHECK: {{.*}}DISubprogram{{.*}}name: "foo"{{.*}}DIFlagAllCallsDescribed{{.*}}
+
+#[no_mangle]
+#[inline(never)]
+pub fn foo(x: i32) -> i32 {
+    bar(x + 1)
+}
+
+#[no_mangle]
+#[inline(never)]
+pub fn bar(x: i32) -> i32 {
+    x * 2
+}