[Mlir-commits] [llvm] [mlir] [OMPIRBuilder][OpenMP][LLVM] Modify and use ReplaceConstant utility in convertTarget (PR #94541)

[Nikita Popov]

================
@@ -5191,17 +5171,23 @@ static Function *createOutlinedFunction(
 
     // Things like GEP's can come in the form of Constants. Constants and
     // ConstantExpr's do not have access to the knowledge of what they're
-    // contained in, so we must dig a little to find an instruction so we can
-    // tell if they're used inside of the function we're outlining. We also
-    // replace the original constant expression with a new instruction
+    // contained in, so we must dig a little to find an instruction so we
+    // can tell if they're used inside of the function we're outlining. We
+    // also replace the original constant expression with a new instruction
     // equivalent; an instruction as it allows easy modification in the
-    // following loop, as we can now know the constant (instruction) is owned by
-    // our target function and replaceUsesOfWith can now be invoked on it
-    // (cannot do this with constants it seems). A brand new one also allows us
-    // to be cautious as it is perhaps possible the old expression was used
-    // inside of the function but exists and is used externally (unlikely by the
-    // nature of a Constant, but still).
-    replaceConstantValueUsesInFuncWithInstr(Input, Func);
+    // following loop, as we can now know the constant (instruction) is
+    // owned by our target function and replaceUsesOfWith can now be invoked
+    // on it (cannot do this with constants it seems). A brand new one also
+    // allows us to be cautious as it is perhaps possible the old expression
+    // was used inside of the function but exists and is used externally
+    // (unlikely by the nature of a Constant, but still).
+    // NOTE: We cannot remove dead constants that have been rewritten to
+    // instructions at this stage, we run the risk of breaking later lowering
+    // by doing so as we could still be in the process of lowering the module
+    // from MLIR to LLVM-IR and the MLIR lowering may still require the original
+    // constants we have created rewritten versions of.
+    if (auto *Const = dyn_cast<Constant>(Input))
+      convertUsersOfConstantsToInstructions({Const}, Func, false);
----------------
nikic wrote:

```suggestion
      convertUsersOfConstantsToInstructions(Const, Func, false);
```
ArrayRef has a single-value overload.

https://github.com/llvm/llvm-project/pull/94541