Add support for alignment annotations to the LLVM dialect to LLVM translation.

[herhut]

Summary

With this change, a function argument attribute of the form
"llvm.align" = <int> will be translated to the corresponding align
attribute in LLVM by the ModuleConversion.

[herhut]

Resolve copy and paste error...

[ftynse]

mlir/lib/Target/LLVMIR/ModuleTranslation.cpp

729

I don't see this verification. It should be somewhere in LLVMDialect::verifyRegionArgAttribute I suppose. The special handling for noalias is necessary here because we had users that would put llvm.noalias on a memref, and then have it propagated to all components of the memref descriptor. Not sure if these still exist...

734

Please add a test for the user-visible error message

[herhut]

add missing changes and test.

[herhut]

PTAL

[ftynse]

Thanks!

mlir/lib/Target/LLVMIR/ModuleTranslation.cpp

if (auto attr = func.getArgAttrOfType<BoolAttr>(argIdx, "llvm.noalias")) {
       // attach the attribute to this argument, based on its type.
       auto argTy = mlirArg.getType().dyn_cast<LLVM::LLVMType>();
       if (!argTy.getUnderlyingType()->isPointerTy())
         return func.emitError(
             "llvm.noalias attribute attached to LLVM non-pointer argument");
       if (attr.getValue())
         llvmArg.addAttr(llvm::Attribute::AttrKind::NoAlias);
     }
+
+    if (auto attr = func.getArgAttrOfType<IntegerAttr>(argIdx, "llvm.align")) {
+      // NB: Attribute already verified to be int, so check if we can indeed
+      // attach the attribute to this argument, based on its type.
+      auto argTy = mlirArg.getType().dyn_cast<LLVM::LLVMType>();
+      if (!argTy.getUnderlyingType()->isPointerTy())
+        return func.emitError(
+            "llvm.align attribute attached to LLVM non-pointer argument");
+      llvmArg.addAttrs(
+          llvm::AttrBuilder().addAlignmentAttr(llvm::Align(attr.getInt())));
+    }
+
     valueMapping[mlirArg] = &llvmArg;
     argIdx++;
   }
 
   // Check the personality and set it.
   if (func.personality().hasValue()) {
     llvm::Type *ty = llvm::Type::getInt8PtrTy(llvmFunc->getContext());
     if (llvm::Constant *pfunc =

mlir/test/Target/llvmir.mlir

// CHECK-NEXT:   br label %3
   llvm.br ^bb1(%arg1 : !llvm.i1)
 }
 
 // CHECK-LABEL: define void @llvm_noalias(float* noalias {{%*.}})
 llvm.func @llvm_noalias(%arg0: !llvm<"float*"> {llvm.noalias = true}) {
   llvm.return
 }
 
+// CHECK-LABEL: define void @llvm_align(float* align 4 {{%*.}})
+llvm.func @llvm_align(%arg0: !llvm<"float*"> {llvm.align = 4}) {
+  llvm.return
+}
+
 // CHECK-LABEL: @llvm_varargs(...)
 llvm.func @llvm_varargs(...)
 
 llvm.func @intpointerconversion(%arg0 : !llvm.i32) -> !llvm.i32 {
 // CHECK:      %2 = inttoptr i32 %0 to i32*
 // CHECK-NEXT: %3 = ptrtoint i32* %2 to i32
   %1 = llvm.inttoptr %arg0 : !llvm.i32 to !llvm<"i32*">
   %2 = llvm.ptrtoint %1 : !llvm<"i32*"> to !llvm.i32