[clang] [llvm] [mlir] [OpenMP] Preserve host capture lifetimes in frontend lowering (PR #218453)

[Tomas Matheson via llvm-commits]

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@@ -1897,6 +1897,16 @@ hostParallelCallback(OpenMPIRBuilder *OMPIRBuilder, Function &OutlinedFn,
          "Expected at least tid and bounded tid as arguments");
   unsigned NumCapturedVars = OutlinedFn.arg_size() - /* tid & bounded tid */ 2;
 
+  // CodeExtractor packs all captures into a fresh structure owned by the
+  // caller. Only this argument exposes the structure to the outlined function,
+  // and the synchronous fork keeps it alive until all callbacks return. These
+  // attributes describe the structure, not the objects its fields point to.
+  if (NumCapturedVars) {
+    assert(NumCapturedVars == 1 && "Expected an aggregate capture argument");
+    OutlinedFn.addParamAttr(2, Attribute::NoAlias);
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tommat01 wrote:

I also added another assert

https://github.com/llvm/llvm-project/pull/218453