[flang] Fix seg fault CodeGenAction::executeAction()

[ergawy]

If generateLLVMIR() fails, we still continue using the module we failed to generate which causes a seg fault if LLVM code-gen failed for some reason or another. This commit fixes this issue.

[llvmbot]

@llvm/pr-subscribers-flang-driver

Author: Kareem Ergawy (ergawy)

Changes

If generateLLVMIR() fails, we still continue using the module we failed to generate which causes a seg fault if LLVM code-gen failed for some reason or another. This commit fixes this issue.

---

Full diff: https://github.com/llvm/llvm-project/pull/78269.diff

1 Files Affected:

• (modified) flang/lib/Frontend/FrontendActions.cpp (+5)

diff --git a/flang/lib/Frontend/FrontendActions.cpp b/flang/lib/Frontend/FrontendActions.cpp
index 74e3992d5ab62ba..65c4df7388f97b2 100644
--- a/flang/lib/Frontend/FrontendActions.cpp
+++ b/flang/lib/Frontend/FrontendActions.cpp
@@ -1202,6 +1202,11 @@ void CodeGenAction::executeAction() {
   if (!llvmModule)
     generateLLVMIR();
 
+  // If generating the LLVM module failed, abort! No need for further error
+  // reporting since generateLLVMIR() does this already.
+  if (!llvmModule)
+    return;
+
   // Set the triple based on the targetmachine (this comes compiler invocation
   // and the command-line target option if specified, or the default if not
   // given on the command-line).

[ergawy]

Note that I came across this issue while testing:

flang-new -c -fopenmp target.f90

For this input:

subroutine omp_target_enter_nowait
   integer :: a(1024)
   !$omp target enter data map(to: a) nowait
end subroutine omp_target_enter_nowait

Now, I get this error (without the seg fault):

error: loc("/home/kaergawy/playground/tmp/target.f90":3:10): LLVM Translation failed for operation: omp.target_enter_data
error: failed to create the LLVM module

nowait seems to be the culprit. Removing it resolves the error.

I am currently looking into this issue and will hopefully open a separate PR.

Edit: this happens because nowait is not supported in CodeGen yet. I forgot about this. Will open a PR with this commit for slightly better error reporting.

[banach-space]

Thanks!

It would be good to add a diagnostic and a test - perhaps trying compiling a "broken" MLIR file?

[ergawy]

Thanks!

It would be good to add a diagnostic and a test - perhaps trying compiling a "broken" MLIR file?

Thanks for the reply @banach-space. I can try to add a unit test (I see there is none for the flang CodeGenAction class so far. I think this will be better self-contained and easier to understand what is going on than a lit test. WDYT?

[banach-space]

Thanks!
It would be good to add a diagnostic and a test - perhaps trying compiling a "broken" MLIR file?

Thanks for the reply @banach-space. I can try to add a unit test (I see there is none for the flang CodeGenAction class so far. I think this will be better self-contained and easier to understand what is going on than a lit test. WDYT?

+1 :)

[ergawy]

Thanks!

It would be good to add a diagnostic and a test - perhaps trying compiling a "broken" MLIR file?

Done!

[ergawy]

Ping! :)

[banach-space]

Very clever - love this approach :)

LGTM, thank you!