LLVM dialect and translation: support global strings

Unlike regular constant values, strings must be placed in some memory and
referred to through a pointer to that memory.  Until now, they were not
supported in function-local constant declarations with `llvm.constant`.
Introduce support for global strings using `llvm.global`, which would translate
them into global arrays in LLVM IR and thus make sure they have some memory
allocated for storage.

PiperOrigin-RevId: 262569316

1 files changed, 11 insertions, 0 deletions

diff --git a/mlir/lib/Target/LLVMIR/ModuleTranslation.cpp b/mlir/lib/Target/LLVMIR/ModuleTranslation.cpp
index bf43848c9ef..3cbf543bdfc 100644
--- a/mlir/lib/Target/LLVMIR/ModuleTranslation.cpp
+++ b/mlir/lib/Target/LLVMIR/ModuleTranslation.cpp
@@ -292,6 +292,17 @@ bool ModuleTranslation::convertBlock(Block &bb, bool ignoreArguments) {
 // Create named global variables that correspond to llvm.global definitions.
 void ModuleTranslation::convertGlobals() {
   for (auto op : mlirModule.getOps<LLVM::GlobalOp>()) {
+    // String attributes are treated separately because they cannot appear as
+    // in-function constants and are thus not supported by getLLVMConstant.
+    if (auto strAttr = op.value().dyn_cast<StringAttr>()) {
+      llvm::Constant *cst = llvm::ConstantDataArray::getString(
+          llvmModule->getContext(), strAttr.getValue(), /*AddNull=*/false);
+      new llvm::GlobalVariable(*llvmModule, cst->getType(), op.constant(),
+                               llvm::GlobalValue::InternalLinkage, cst,
+                               op.sym_name());
+      return;
+    }
+
     llvm::Type *type = op.getType().getUnderlyingType();
     new llvm::GlobalVariable(
         *llvmModule, type, op.constant(), llvm::GlobalValue::InternalLinkage,