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[mlir] don't drop undef initializers in translation to LLVM IR

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LLVM IR allows globals with external linkage to have initializers, including
undef. The translation was incorrectly using undef as a indicator that the
initializer should be ignored in translation, leading to the impossibility to
create an external global with an explicit undef initializer. Fix this and use
nullptr as a marker instead.

Reviewed By: wsmoses

Differential Revision: https://reviews.llvm.org/D105631
This commit is contained in:
Alex Zinenko
2021-07-08 16:07:09 +02:00
parent 42cc7f3c52
commit d4df3825bd
2 changed files with 23 additions and 7 deletions
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24
mlir/lib/Target/LLVMIR/ModuleTranslation.cpp
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@@ -415,11 +415,13 @@ static Block &getModuleBody(Operation *module) {
}
/// A helper method to decide if a constant must not be set as a global variable
/// initializer.
/// initializer. For an external linkage variable, the variable with an
/// initializer is considered externally visible and defined in this module, the
/// variable without an initializer is externally available and is defined
/// elsewhere.
static bool shouldDropGlobalInitializer(llvm::GlobalValue::LinkageTypes linkage,
llvm::Constant *cst) {
return (linkage == llvm::GlobalVariable::ExternalLinkage &&
isa<llvm::UndefValue>(cst)) ||
return (linkage == llvm::GlobalVariable::ExternalLinkage && !cst) ||
linkage == llvm::GlobalVariable::ExternalWeakLinkage;
}
@@ -436,7 +438,7 @@ static void addRuntimePreemptionSpecifier(bool dsoLocalRequested,
LogicalResult ModuleTranslation::convertGlobals() {
for (auto op : getModuleBody(mlirModule).getOps<LLVM::GlobalOp>()) {
llvm::Type *type = convertType(op.getType());
llvm::Constant *cst = llvm::UndefValue::get(type);
llvm::Constant *cst = nullptr;
if (op.getValueOrNull()) {
// String attributes are treated separately because they cannot appear as
// in-function constants and are thus not supported by getLLVMConstant.
@@ -452,10 +454,18 @@ LogicalResult ModuleTranslation::convertGlobals() {
auto linkage = convertLinkageToLLVM(op.linkage());
auto addrSpace = op.addr_space();
// LLVM IR requires constant with linkage other than external or weak
// external to have initializers. If MLIR does not provide an initializer,
// default to undef.
bool dropInitializer = shouldDropGlobalInitializer(linkage, cst);
if (!dropInitializer && !cst)
cst = llvm::UndefValue::get(type);
else if (dropInitializer && cst)
cst = nullptr;
auto *var = new llvm::GlobalVariable(
*llvmModule, type, op.constant(), linkage,
shouldDropGlobalInitializer(linkage, cst) ? nullptr : cst,
op.sym_name(),
*llvmModule, type, op.constant(), linkage, cst, op.sym_name(),
/*InsertBefore=*/nullptr, llvm::GlobalValue::NotThreadLocal, addrSpace);
if (op.unnamed_addr().hasValue())

6
mlir/test/Target/LLVMIR/llvmir.mlir
View File

@@ -36,6 +36,12 @@ llvm.mlir.global internal constant @string_const("foobar") : !llvm.array<6 x i8>
// CHECK: @int_global_undef = internal global i64 undef
llvm.mlir.global internal @int_global_undef() : i64
// CHECK: @explicit_undef = global i32 undef
llvm.mlir.global external @explicit_undef() : i32 {
%0 = llvm.mlir.undef : i32
llvm.return %0 : i32
}
// CHECK: @int_gep = internal constant i32* getelementptr (i32, i32* @i32_global, i32 2)
llvm.mlir.global internal constant @int_gep() : !llvm.ptr<i32> {
%addr = llvm.mlir.addressof @i32_global : !llvm.ptr<i32>