[rustllvm] Use report_fatal_error over llvm_unreachable

This makes it more robust when assertions are disabled,
crashing instead of causing UB.

Also introduces a tidy check to enforce this rule,
which in turn necessitated making tidy run on src/rustllvm.

Fixes #44020

5 files changed, 37 insertions, 30 deletions

diff --git a/src/rustllvm/ArchiveWrapper.cpp b/src/rustllvm/ArchiveWrapper.cpp
index 7f76861c077..591ebdc9ddb 100644
--- a/src/rustllvm/ArchiveWrapper.cpp
+++ b/src/rustllvm/ArchiveWrapper.cpp
@@ -66,7 +66,7 @@ static Archive::Kind fromRust(LLVMRustArchiveKind Kind) {
   case LLVMRustArchiveKind::COFF:
     return Archive::K_COFF;
   default:
-    llvm_unreachable("Bad ArchiveKind.");
+    report_fatal_error("Bad ArchiveKind.");
   }
 }
 
diff --git a/src/rustllvm/PassWrapper.cpp b/src/rustllvm/PassWrapper.cpp
index d0c042e6451..4a359fb3ad3 100644
--- a/src/rustllvm/PassWrapper.cpp
+++ b/src/rustllvm/PassWrapper.cpp
@@ -235,7 +235,7 @@ static CodeModel::Model fromRust(LLVMRustCodeModel Model) {
   case LLVMRustCodeModel::Large:
     return CodeModel::Large;
   default:
-    llvm_unreachable("Bad CodeModel.");
+    report_fatal_error("Bad CodeModel.");
   }
 }
 
@@ -258,7 +258,7 @@ static CodeGenOpt::Level fromRust(LLVMRustCodeGenOptLevel Level) {
   case LLVMRustCodeGenOptLevel::Aggressive:
     return CodeGenOpt::Aggressive;
   default:
-    llvm_unreachable("Bad CodeGenOptLevel.");
+    report_fatal_error("Bad CodeGenOptLevel.");
   }
 }
 
@@ -302,7 +302,7 @@ static Optional<Reloc::Model> fromRust(LLVMRustRelocMode RustReloc) {
     break;
 #endif
   }
-  llvm_unreachable("Bad RelocModel.");
+  report_fatal_error("Bad RelocModel.");
 }
 
 #if LLVM_RUSTLLVM
@@ -511,7 +511,7 @@ static TargetMachine::CodeGenFileType fromRust(LLVMRustFileType Type) {
   case LLVMRustFileType::ObjectFile:
     return TargetMachine::CGFT_ObjectFile;
   default:
-    llvm_unreachable("Bad FileType.");
+    report_fatal_error("Bad FileType.");
   }
 }
 
@@ -1197,7 +1197,7 @@ extern "C" bool
 LLVMRustWriteThinBitcodeToFile(LLVMPassManagerRef PMR,
                                LLVMModuleRef M,
                                const char *BcFile) {
-  llvm_unreachable("ThinLTO not available");
+  report_fatal_error("ThinLTO not available");
 }
 
 struct LLVMRustThinLTOData {
@@ -1211,32 +1211,32 @@ LLVMRustCreateThinLTOData(LLVMRustThinLTOModule *modules,
                           int num_modules,
                           const char **preserved_symbols,
                           int num_symbols) {
-  llvm_unreachable("ThinLTO not available");
+  report_fatal_error("ThinLTO not available");
 }
 
 extern "C" bool
 LLVMRustPrepareThinLTORename(const LLVMRustThinLTOData *Data, LLVMModuleRef M) {
-  llvm_unreachable("ThinLTO not available");
+  report_fatal_error("ThinLTO not available");
 }
 
 extern "C" bool
 LLVMRustPrepareThinLTOResolveWeak(const LLVMRustThinLTOData *Data, LLVMModuleRef M) {
-  llvm_unreachable("ThinLTO not available");
+  report_fatal_error("ThinLTO not available");
 }
 
 extern "C" bool
 LLVMRustPrepareThinLTOInternalize(const LLVMRustThinLTOData *Data, LLVMModuleRef M) {
-  llvm_unreachable("ThinLTO not available");
+  report_fatal_error("ThinLTO not available");
 }
 
 extern "C" bool
 LLVMRustPrepareThinLTOImport(const LLVMRustThinLTOData *Data, LLVMModuleRef M) {
-  llvm_unreachable("ThinLTO not available");
+  report_fatal_error("ThinLTO not available");
 }
 
 extern "C" void
 LLVMRustFreeThinLTOData(LLVMRustThinLTOData *Data) {
-  llvm_unreachable("ThinLTO not available");
+  report_fatal_error("ThinLTO not available");
 }
 
 struct LLVMRustThinLTOBuffer {
@@ -1244,22 +1244,22 @@ struct LLVMRustThinLTOBuffer {
 
 extern "C" LLVMRustThinLTOBuffer*
 LLVMRustThinLTOBufferCreate(LLVMModuleRef M) {
-  llvm_unreachable("ThinLTO not available");
+  report_fatal_error("ThinLTO not available");
 }
 
 extern "C" void
 LLVMRustThinLTOBufferFree(LLVMRustThinLTOBuffer *Buffer) {
-  llvm_unreachable("ThinLTO not available");
+  report_fatal_error("ThinLTO not available");
 }
 
 extern "C" const void*
 LLVMRustThinLTOBufferPtr(const LLVMRustThinLTOBuffer *Buffer) {
-  llvm_unreachable("ThinLTO not available");
+  report_fatal_error("ThinLTO not available");
 }
 
 extern "C" size_t
 LLVMRustThinLTOBufferLen(const LLVMRustThinLTOBuffer *Buffer) {
-  llvm_unreachable("ThinLTO not available");
+  report_fatal_error("ThinLTO not available");
 }
 
 extern "C" LLVMModuleRef
@@ -1267,6 +1267,6 @@ LLVMRustParseBitcodeForThinLTO(LLVMContextRef Context,
                                const char *data,
                                size_t len,
                                const char *identifier) {
-  llvm_unreachable("ThinLTO not available");
+  report_fatal_error("ThinLTO not available");
 }
 #endif // LLVM_VERSION_GE(4, 0)
diff --git a/src/rustllvm/RustWrapper.cpp b/src/rustllvm/RustWrapper.cpp
index 9aa172591b8..424b226bcf7 100644
--- a/src/rustllvm/RustWrapper.cpp
+++ b/src/rustllvm/RustWrapper.cpp
@@ -54,7 +54,7 @@ static AtomicOrdering fromRust(LLVMAtomicOrdering Ordering) {
     return AtomicOrdering::SequentiallyConsistent;
   }
 
-  llvm_unreachable("Invalid LLVMAtomicOrdering value!");
+  report_fatal_error("Invalid LLVMAtomicOrdering value!");
 }
 
 static LLVM_THREAD_LOCAL char *LastError;
@@ -161,7 +161,7 @@ static Attribute::AttrKind fromRust(LLVMRustAttribute Kind) {
   case SanitizeMemory:
     return Attribute::SanitizeMemory;
   }
-  llvm_unreachable("bad AttributeKind");
+  report_fatal_error("bad AttributeKind");
 }
 
 extern "C" void LLVMRustAddCallSiteAttribute(LLVMValueRef Instr, unsigned Index,
@@ -356,7 +356,7 @@ static SyncScope::ID fromRust(LLVMRustSynchronizationScope Scope) {
   case LLVMRustSynchronizationScope::CrossThread:
     return SyncScope::System;
   default:
-    llvm_unreachable("bad SynchronizationScope.");
+    report_fatal_error("bad SynchronizationScope.");
   }
 }
 #else
@@ -367,7 +367,7 @@ static SynchronizationScope fromRust(LLVMRustSynchronizationScope Scope) {
   case LLVMRustSynchronizationScope::CrossThread:
     return CrossThread;
   default:
-    llvm_unreachable("bad SynchronizationScope.");
+    report_fatal_error("bad SynchronizationScope.");
   }
 }
 #endif
@@ -397,7 +397,7 @@ static InlineAsm::AsmDialect fromRust(LLVMRustAsmDialect Dialect) {
   case LLVMRustAsmDialect::Intel:
     return InlineAsm::AD_Intel;
   default:
-    llvm_unreachable("bad AsmDialect.");
+    report_fatal_error("bad AsmDialect.");
   }
 }
 
@@ -748,7 +748,7 @@ extern "C" LLVMMetadataRef LLVMRustDIBuilderCreateVariable(
         unwrapDI<DIType>(Ty), AlwaysPreserve, fromRust(Flags)
 #if LLVM_VERSION_GE(4, 0)
         ,
-	AlignInBits
+  AlignInBits
 #endif
         ));
   } else {
@@ -1149,7 +1149,7 @@ extern "C" LLVMTypeKind LLVMRustGetTypeKind(LLVMTypeRef Ty) {
     return LLVMTokenTypeKind;
 #endif
   }
-  llvm_unreachable("Unhandled TypeID.");
+  report_fatal_error("Unhandled TypeID.");
 }
 
 extern "C" void LLVMRustWriteDebugLocToString(LLVMContextRef C,
@@ -1370,7 +1370,7 @@ static LLVMRustLinkage toRust(LLVMLinkage Linkage) {
   case LLVMCommonLinkage:
     return LLVMRustLinkage::CommonLinkage;
   default:
-    llvm_unreachable("Invalid LLVMRustLinkage value!");
+    report_fatal_error("Invalid LLVMRustLinkage value!");
   }
 }
 
@@ -1399,7 +1399,7 @@ static LLVMLinkage fromRust(LLVMRustLinkage Linkage) {
   case LLVMRustLinkage::CommonLinkage:
     return LLVMCommonLinkage;
   }
-  llvm_unreachable("Invalid LLVMRustLinkage value!");
+  report_fatal_error("Invalid LLVMRustLinkage value!");
 }
 
 extern "C" LLVMRustLinkage LLVMRustGetLinkage(LLVMValueRef V) {
@@ -1447,7 +1447,7 @@ static LLVMRustVisibility toRust(LLVMVisibility Vis) {
   case LLVMProtectedVisibility:
     return LLVMRustVisibility::Protected;
   }
-  llvm_unreachable("Invalid LLVMRustVisibility value!");
+  report_fatal_error("Invalid LLVMRustVisibility value!");
 }
 
 static LLVMVisibility fromRust(LLVMRustVisibility Vis) {
@@ -1459,7 +1459,7 @@ static LLVMVisibility fromRust(LLVMRustVisibility Vis) {
   case LLVMRustVisibility::Protected:
     return LLVMProtectedVisibility;
   }
-  llvm_unreachable("Invalid LLVMRustVisibility value!");
+  report_fatal_error("Invalid LLVMRustVisibility value!");
 }
 
 extern "C" LLVMRustVisibility LLVMRustGetVisibility(LLVMValueRef V) {
diff --git a/src/tools/tidy/src/lib.rs b/src/tools/tidy/src/lib.rs
index 598620fa293..bd49f288eb2 100644
--- a/src/tools/tidy/src/lib.rs
+++ b/src/tools/tidy/src/lib.rs
@@ -57,7 +57,6 @@ fn filter_dirs(path: &Path) -> bool {
         "src/libbacktrace",
         "src/libcompiler_builtins",
         "src/compiler-rt",
-        "src/rustllvm",
         "src/liblibc",
         "src/vendor",
         "src/rt/hoedown",
diff --git a/src/tools/tidy/src/style.rs b/src/tools/tidy/src/style.rs
index a689d8a8be4..40d84b98d3a 100644
--- a/src/tools/tidy/src/style.rs
+++ b/src/tools/tidy/src/style.rs
@@ -50,6 +50,11 @@ const UNEXPLAINED_IGNORE_DOCTEST_INFO: &str = r#"unexplained "```ignore" doctest
 
 "#;
 
+const LLVM_UNREACHABLE_INFO: &str = r"\
+C++ code used llvm_unreachable, which triggers undefined behavior
+when executed when assertions are disabled.
+Use llvm::report_fatal_error for increased robustness.";
+
 /// Parser states for line_is_url.
 #[derive(PartialEq)]
 #[allow(non_camel_case_types)]
@@ -108,7 +113,7 @@ pub fn check(path: &Path, bad: &mut bool) {
     let mut contents = String::new();
     super::walk(path, &mut super::filter_dirs, &mut |file| {
         let filename = file.file_name().unwrap().to_string_lossy();
-        let extensions = [".rs", ".py", ".js", ".sh", ".c", ".h"];
+        let extensions = [".rs", ".py", ".js", ".sh", ".c", ".cpp", ".h"];
         if extensions.iter().all(|e| !filename.ends_with(e)) ||
            filename.starts_with(".#") {
             return
@@ -153,6 +158,9 @@ pub fn check(path: &Path, bad: &mut bool) {
             if line.ends_with("```ignore") || line.ends_with("```rust,ignore") {
                 err(UNEXPLAINED_IGNORE_DOCTEST_INFO);
             }
+            if filename.ends_with(".cpp") && line.contains("llvm_unreachable") {
+                err(LLVM_UNREACHABLE_INFO);
+            }
         }
         if !licenseck(file, &contents) {
             tidy_error!(bad, "{}: incorrect license", file.display());