[Mlir-commits] [mlir] [MLIR][LLVM] Fix crash in LLVMFunctionType::clone when erasing void function results (PR #185093)

[Mehdi Amini]

https://github.com/joker-eph updated https://github.com/llvm/llvm-project/pull/185093

>From 0b92e6668ab60943c618030f947fee65dcd5c911 Mon Sep 17 00:00:00 2001
From: Mehdi Amini <joker.eph at gmail.com>
Date: Fri, 6 Mar 2026 09:45:15 -0800
Subject: [PATCH] [MLIR][LLVM] Fix crash in LLVMFunctionType::clone when
 erasing void function results

LLVMFunctionType::clone(inputs, results) was asserting that results.size() == 1,
which caused a crash (later changed to return null/failure) when erasing results
from a void llvm.func via FunctionOpInterface::eraseResults.

For LLVM function types, an empty results range maps to void return: the
FunctionOpInterface represents void llvm.func with 0 results, while the
underlying LLVMFunctionType stores an explicit LLVMVoidType. When erasing
all results (or no-op erasing 0 results from a void function), the interface
passes an empty TypeRange to clone(), which should produce a void function type.

Fix by accepting an empty results range in LLVMFunctionType::clone() and
mapping it to LLVMVoidType. More than one result remains invalid.

Update the regression test that previously expected a failure error to instead
verify that erasing no results from a void llvm.func succeeds as a no-op.

Fixes #128322

Assisted-by: Claude Code
---
 mlir/lib/Dialect/LLVMIR/IR/LLVMTypes.cpp | 11 +++++++++--
 mlir/test/IR/test-func-erase-result.mlir |  4 +++-
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/mlir/lib/Dialect/LLVMIR/IR/LLVMTypes.cpp b/mlir/lib/Dialect/LLVMIR/IR/LLVMTypes.cpp
index e24615c8d3046..3a3a7ca63ea13 100644
--- a/mlir/lib/Dialect/LLVMIR/IR/LLVMTypes.cpp
+++ b/mlir/lib/Dialect/LLVMIR/IR/LLVMTypes.cpp
@@ -232,11 +232,18 @@ LLVMFunctionType::getChecked(function_ref<InFlightDiagnostic()> emitError,
 
 LLVMFunctionType LLVMFunctionType::clone(TypeRange inputs,
                                          TypeRange results) const {
-  if (results.size() != 1 || !isValidResultType(results[0]))
+  // LLVM functions have exactly one return type. An empty results range
+  // corresponds to a void return type (as FunctionOpInterface represents void
+  // functions with 0 results). More than one result is not valid.
+  if (results.size() > 1)
+    return {};
+  Type resultType =
+      results.empty() ? LLVMVoidType::get(getContext()) : results[0];
+  if (!isValidResultType(resultType))
     return {};
   if (!llvm::all_of(inputs, isValidArgumentType))
     return {};
-  return get(results[0], llvm::to_vector(inputs), isVarArg());
+  return get(resultType, llvm::to_vector(inputs), isVarArg());
 }
 
 ArrayRef<Type> LLVMFunctionType::getReturnTypes() const {
diff --git a/mlir/test/IR/test-func-erase-result.mlir b/mlir/test/IR/test-func-erase-result.mlir
index a32866227547b..c508daff3c440 100644
--- a/mlir/test/IR/test-func-erase-result.mlir
+++ b/mlir/test/IR/test-func-erase-result.mlir
@@ -69,5 +69,7 @@ func.func private @f() -> (
 
 // -----
 
-// expected-error @below {{failed to erase results}}
+// Erasing no results from a void llvm.func (0 results) is a no-op and should
+// succeed. Previously this crashed with an assertion in LLVMFunctionType::clone.
+// CHECK: llvm.func @llvm_func(!llvm.ptr, i64)
 llvm.func @llvm_func(!llvm.ptr, i64)