[flang-commits] [flang] [flang][runtime] Disable optimization for traceback related functions. (PR #124172)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-flang-runtime

Author: Slava Zakharin (vzakhari)

<details>
<summary>Changes</summary>

The backtrace may at least print the backtrace name in the call stack,
but this does not happen with the release builds of the runtime.
Surprisingly, specifying "no-omit-frame-pointer" did not work
with GCC, so I decided to fall back to -O0 for these functions.


---
Full diff: https://github.com/llvm/llvm-project/pull/124172.diff


2 Files Affected:

- (modified) flang/include/flang/Common/api-attrs.h (+11) 
- (modified) flang/runtime/stop.cpp (+9-5) 


``````````diff
diff --git a/flang/include/flang/Common/api-attrs.h b/flang/include/flang/Common/api-attrs.h
index d73e60996bc81f..1ee91ca8e0d9d3 100644
--- a/flang/include/flang/Common/api-attrs.h
+++ b/flang/include/flang/Common/api-attrs.h
@@ -178,4 +178,15 @@
 #define RT_DEVICE_NOINLINE_HOST_INLINE inline
 #endif
 
+/* RT_OPTNONE_ATTR allows disabling optimizations per function. */
+#if __has_attribute(optimize)
+/* GCC style. */
+#define RT_OPTNONE_ATTR __attribute__((optimize("O0")))
+#elif __has_attribute(optnone)
+/* Clang style. */
+#define RT_OPTNONE_ATTR __attribute__((optnone))
+#else
+#define RT_OPTNONE_ATTR
+#endif
+
 #endif /* !FORTRAN_RUNTIME_API_ATTRS_H_ */
diff --git a/flang/runtime/stop.cpp b/flang/runtime/stop.cpp
index a7be8a082e026b..f8c180e0aaffa1 100644
--- a/flang/runtime/stop.cpp
+++ b/flang/runtime/stop.cpp
@@ -157,7 +157,7 @@ void RTNAME(PauseStatementText)(const char *code, std::size_t length) {
   std::exit(status);
 }
 
-static void PrintBacktrace() {
+static RT_NOINLINE_ATTR void PrintBacktrace() {
 #ifdef HAVE_BACKTRACE
   // TODO: Need to parse DWARF information to print function line numbers
   constexpr int MAX_CALL_STACK{999};
@@ -165,8 +165,12 @@ static void PrintBacktrace() {
   int nptrs{(int)backtrace(buffer, MAX_CALL_STACK)};
 
   if (char **symbols{backtrace_symbols(buffer, nptrs)}) {
-    for (int i = 0; i < nptrs; i++) {
-      Fortran::runtime::Terminator{}.PrintCrashArgs("#%d %s\n", i, symbols[i]);
+    // Skip the PrintBacktrace() frame, as it is just a utility.
+    // It makes sense to start printing the backtrace
+    // from Abort() or backtrace().
+    for (int i = 1; i < nptrs; i++) {
+      Fortran::runtime::Terminator{}.PrintCrashArgs(
+          "#%d %s\n", i - 1, symbols[i]);
     }
     free(symbols);
   }
@@ -179,14 +183,14 @@ static void PrintBacktrace() {
 #endif
 }
 
-[[noreturn]] void RTNAME(Abort)() {
+[[noreturn]] RT_OPTNONE_ATTR void RTNAME(Abort)() {
 #ifdef HAVE_BACKTRACE
   PrintBacktrace();
 #endif
   std::abort();
 }
 
-void FORTRAN_PROCEDURE_NAME(backtrace)() { PrintBacktrace(); }
+RT_OPTNONE_ATTR void FORTRAN_PROCEDURE_NAME(backtrace)() { PrintBacktrace(); }
 
 [[noreturn]] void RTNAME(ReportFatalUserError)(
     const char *message, const char *source, int line) {

``````````

</details>


https://github.com/llvm/llvm-project/pull/124172