[Mlir-commits] [mlir] [mlir] do not inject malloc/free in to-LLVM translation (PR #73224)

[Oleksandr Alex Zinenko]

https://github.com/ftynse created https://github.com/llvm/llvm-project/pull/73224

In the early days of MLIR-to-LLVM IR translation, it had to forcefully inject declarations of `malloc` and `free` functions as then-standard (now `memref`) dialect ops were unconditionally lowering to libc calls. This is no longer the case. Even when they do lower to libc calls, the signatures of those methods are injected at lowering since calls must target declared functions in valid IR. Don't inject those declarations anymore.

>From 081c87cef14370d20121454b02b4e79d3a4f6f62 Mon Sep 17 00:00:00 2001
From: Alex Zinenko <zinenko at google.com>
Date: Thu, 23 Nov 2023 09:44:45 +0000
Subject: [PATCH] [mlir] do not inject malloc/free in to-LLVM translation

In the early days of MLIR-to-LLVM IR translation, it had to forcefully
inject declarations of `malloc` and `free` functions as then-standard
(now `memref`) dialect ops were unconditionally lowering to libc calls.
This is no longer the case. Even when they do lower to libc calls, the
signatures of those methods are injected at lowering since calls must
target declared functions in valid IR. Don't inject those declarations
anymore.
---
 mlir/lib/Target/LLVMIR/ModuleTranslation.cpp | 8 --------
 mlir/test/Target/LLVMIR/llvmir.mlir          | 2 +-
 2 files changed, 1 insertion(+), 9 deletions(-)

diff --git a/mlir/lib/Target/LLVMIR/ModuleTranslation.cpp b/mlir/lib/Target/LLVMIR/ModuleTranslation.cpp
index ef1c8c21d54b08f..c5df0c7ec181a7c 100644
--- a/mlir/lib/Target/LLVMIR/ModuleTranslation.cpp
+++ b/mlir/lib/Target/LLVMIR/ModuleTranslation.cpp
@@ -1320,14 +1320,6 @@ prepareLLVMModule(Operation *m, llvm::LLVMContext &llvmContext,
           m->getDiscardableAttr(LLVM::LLVMDialect::getTargetTripleAttrName()))
     llvmModule->setTargetTriple(cast<StringAttr>(targetTripleAttr).getValue());
 
-  // Inject declarations for `malloc` and `free` functions that can be used in
-  // memref allocation/deallocation coming from standard ops lowering.
-  llvm::IRBuilder<> builder(llvmContext);
-  llvmModule->getOrInsertFunction("malloc", builder.getInt8PtrTy(),
-                                  builder.getInt64Ty());
-  llvmModule->getOrInsertFunction("free", builder.getVoidTy(),
-                                  builder.getInt8PtrTy());
-
   return llvmModule;
 }
 
diff --git a/mlir/test/Target/LLVMIR/llvmir.mlir b/mlir/test/Target/LLVMIR/llvmir.mlir
index 73fcee0dd2e70bd..ab8506ff163efe6 100644
--- a/mlir/test/Target/LLVMIR/llvmir.mlir
+++ b/mlir/test/Target/LLVMIR/llvmir.mlir
@@ -179,7 +179,7 @@ llvm.mlir.global internal constant @sectionvar("teststring")  {section = ".mysec
 // CHECK: declare ptr @malloc(i64)
 llvm.func @malloc(i64) -> !llvm.ptr
 // CHECK: declare void @free(ptr)
-
+llvm.func @free(!llvm.ptr)
 
 //
 // Basic functionality: function and block conversion, function calls,