[flang-commits] [flang] [Flang] [OpenMP] Run `MarkDeclareTarget` pass again after `ConvertMathToFuncs` (PR #210049)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-flang-fir-hlfir

Author: Soham Karandikar (skadewdl3)

<details>
<summary>Changes</summary>

Fixes #<!-- -->209123.

The power operation `math.ipowi` is converted to a function by `ConvertMathToFuncs`. When used in a target region, this pass runs well after `MarkDeclareTarget` which causes the newly created power function to not have the `omp.declare_target` attribute - thus causing lowering issues. Detailed investigation [here](https://github.com/llvm/llvm-project/issues/209123#issuecomment-4991765854).

Right now, I've just added a couple of lines to run `MarkDeclareTarget` again, after `ConvertMathToFuncs`. Since I'm quite new to this, I'd like some help on whether this is acceptable, or should the `MarkDeclareTarget` pass be moved to after `ConvertMathToFuncs`.

---
Full diff: https://github.com/llvm/llvm-project/pull/210049.diff


1 Files Affected:

- (modified) flang/lib/Optimizer/Passes/Pipelines.cpp (+5) 


``````````diff
diff --git a/flang/lib/Optimizer/Passes/Pipelines.cpp b/flang/lib/Optimizer/Passes/Pipelines.cpp
index 879a224824119..7fe8bccc14d54 100644
--- a/flang/lib/Optimizer/Passes/Pipelines.cpp
+++ b/flang/lib/Optimizer/Passes/Pipelines.cpp
@@ -464,6 +464,11 @@ void createDefaultFIRCodeGenPassPipeline(mlir::PassManager &pm,
   pm.addPass(fir::createEmitMIFGlobalCtors());
 
   if (config.EnableOpenMP && !config.EnableOpenMPSimd) {
+    // Since some math operations may be converted to function calls by the
+    // ConvertMathToFuncs pass, we need to mark them with the omp.declare_target
+    // attribute if they're called from a target region.
+    pm.addPass(mlir::omp::createMarkDeclareTargetPass());
+
     // Remove all non target-related operations from host functions still
     // remaining at this point, if compiling for an OpenMP target device. This
     // is required before translating 'omp' dialect operations to LLVM IR.

``````````

</details>


https://github.com/llvm/llvm-project/pull/210049