[CIR] Replace uses of global with alias

[badumbatish]

Fixes #1809

[github-actions]

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff HEAD~1 HEAD --extensions cpp -- clang/lib/CIR/CodeGen/CIRGenModule.cpp mlir/lib/Dialect/LLVMIR/IR/LLVMDialect.cpp

View the diff from clang-format here.

diff --git a/mlir/lib/Dialect/LLVMIR/IR/LLVMDialect.cpp b/mlir/lib/Dialect/LLVMIR/IR/LLVMDialect.cpp
index bc81f93b7b..ebfa6a6b0b 100644
--- a/mlir/lib/Dialect/LLVMIR/IR/LLVMDialect.cpp
+++ b/mlir/lib/Dialect/LLVMIR/IR/LLVMDialect.cpp
@@ -1184,7 +1184,7 @@ LogicalResult CallOp::verifySymbolUses(SymbolTableCollection &symbolTable) {
       fnType = fn.getFunctionType();
     } else if (auto ifunc = dyn_cast<IFuncOp>(callee)) {
       fnType = ifunc.getIFuncType();
-    } else if (auto aliasFn = dyn_cast<AliasOp>(callee)){
+    } else if (auto aliasFn = dyn_cast<AliasOp>(callee)) {
       fnType = aliasFn.getType();
     } else {
       return emitOpError()

[badumbatish]

i'm putting up a temp commit to gather reviews if i'm heading in the right direction. Right now the implementation is hitting a verification error on the following test case but i'm not really sure why

class A {
public:
  A();
} A;
A::A() {}

the LLVM IR module before lowering to LLVM and the LLVM module before verification is this.

ninja -C build && ./build/bin/clang --target=x86_64-unknown-linux  -S scratch/global_alias.cpp  -o - --sysroot=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.4.sdk -emit-llvm -fclangir

ninja: Entering directory `build'
[17/17] Linking CXX shared library lib/libclang-cpp.dylib
module @"/Users/jjasmine/Developer/igalia/clangir/scratch/global_alias.cpp" attributes {cir.global_ctors = [#cir.global_ctor<"__cxx_global_var_init", 65535>], cir.type_size_info = #cir.type_size_info<char = 8, int = 32, size_t = 64>, cir.uwtable = #cir.uwtable<async>, dlti.dl_spec = #dlti.dl_spec<!llvm.ptr<270> = dense<32> : vector<4xi64>, !llvm.ptr<271> = dense<32> : vector<4xi64>, !llvm.ptr<272> = dense<64> : vector<4xi64>, i64 = dense<64> : vector<2xi64>, i128 = dense<128> : vector<2xi64>, f80 = dense<128> : vector<2xi64>, !llvm.ptr = dense<64> : vector<4xi64>, i1 = dense<8> : vector<2xi64>, i8 = dense<8> : vector<2xi64>, i16 = dense<16> : vector<2xi64>, i32 = dense<32> : vector<2xi64>, f16 = dense<16> : vector<2xi64>, f64 = dense<64> : vector<2xi64>, f128 = dense<128> : vector<2xi64>, "dlti.endianness" = "little", "dlti.mangling_mode" = "e", "dlti.legal_int_widths" = array<i32: 8, 16, 32, 64>, "dlti.stack_alignment" = 128 : i64>, llvm.target_triple = "x86_64-unknown-linux"} {
  llvm.mlir.global external @A() {addr_space = 0 : i32, alignment = 1 : i64, dso_local} : !llvm.struct<"class.A", (i8)> {
    %0 = llvm.mlir.zero : !llvm.struct<"class.A", (i8)>
    llvm.return %0 : !llvm.struct<"class.A", (i8)>
  }
  llvm.func internal @__cxx_global_var_init() attributes {cir.extra_attrs = #cir<extra({})>, global_visibility = #cir<visibility default>, sym_visibility = "private"} {
    %0 = llvm.mlir.addressof @A : !llvm.ptr
    llvm.call @_ZN1AC1Ev(%0) : (!llvm.ptr) -> ()
    llvm.return
  }
  llvm.func @_ZN1AC2Ev(%arg0: !llvm.ptr) attributes {cir.extra_attrs = #cir<extra({inline = #cir.inline<no>, nothrow = #cir.nothrow, optnone = #cir.optnone, uwtable = #cir.uwtable<async>})>, cxx_special_member = #cir.cxx_ctor<!cir.record<class "A" padded {!cir.int<u, 8>} #cir.record.decl.ast>, default>, dso_local, global_visibility = #cir<visibility default>} {
    %0 = llvm.mlir.constant(1 : index) : i64
    %1 = llvm.alloca %0 x !llvm.ptr {alignment = 8 : i64} : (i64) -> !llvm.ptr
    llvm.store %arg0, %1 {alignment = 8 : i64} : !llvm.ptr, !llvm.ptr
    %2 = llvm.load %1 {alignment = 8 : i64} : !llvm.ptr -> !llvm.ptr
    llvm.return
  }
  llvm.mlir.alias external @_ZN1AC1Ev {aliasee = @_ZN1AC2Ev, cir.extra_attrs = #cir<extra({})>, cxx_special_member = #cir.cxx_ctor<!cir.record<class "A" padded {!cir.int<u, 8>} #cir.record.decl.ast>, default>, dso_local, global_visibility = #cir<visibility default>, sym_visibility = "private"} : !llvm.func<void (ptr)> {
    %0 = llvm.mlir.addressof @_ZN1AC2Ev : !llvm.ptr
    llvm.return %0 : !llvm.ptr
  }
  llvm.func @_GLOBAL__sub_I_global_alias.cpp() attributes {cir.extra_attrs = #cir<extra({})>, global_visibility = #cir<visibility default>, sym_visibility = "private"} {
    llvm.call @__cxx_global_var_init() : () -> ()
    llvm.return
  }
  llvm.mlir.global appending constant @llvm.global_ctors() {addr_space = 0 : i32} : !llvm.array<1 x struct<(i32, ptr, ptr)>> {
    %0 = llvm.mlir.undef : !llvm.array<1 x struct<(i32, ptr, ptr)>>
    %1 = llvm.mlir.undef : !llvm.struct<(i32, ptr, ptr)>
    %2 = llvm.mlir.constant(65535 : i32) : i32
    %3 = llvm.mlir.addressof @__cxx_global_var_init : !llvm.ptr
    %4 = llvm.mlir.zero : !llvm.ptr
    %5 = llvm.insertvalue %2, %1[0] : !llvm.struct<(i32, ptr, ptr)>
    %6 = llvm.insertvalue %3, %5[1] : !llvm.struct<(i32, ptr, ptr)>
    %7 = llvm.insertvalue %4, %6[2] : !llvm.struct<(i32, ptr, ptr)>
    %8 = llvm.insertvalue %7, %0[0] : !llvm.array<1 x struct<(i32, ptr, ptr)>>
    llvm.return %8 : !llvm.array<1 x struct<(i32, ptr, ptr)>>
  }
}
; ModuleID = '/Users/jjasmine/Developer/igalia/clangir/scratch/global_alias.cpp'
source_filename = "/Users/jjasmine/Developer/igalia/clangir/scratch/global_alias.cpp"
target datalayout = "e-m:e-n8:16:32:64-S128-p270:32:32:32:32-p271:32:32:32:32-p272:64:64:64:64-i64:64-i128:128-f80:128-p0:64:64:64:64-i1:8-i8:8-i16:16-i32:32-f16:16-f64:64-f128:128"
target triple = "x86_64-unknown-linux"

%class.A = type { i8 }

@A = dso_local global %class.A zeroinitializer, align 1
@llvm.global_ctors = appending constant [1 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 65535, ptr @__cxx_global_var_init, ptr null }]

@_ZN1AC1Ev = alias void (ptr), ptr @_ZN1AC2Ev

define internal void @__cxx_global_var_init() {
  call <cannot get addrspace!> void <null operand!>(ptr @A)
  ret void
}

; Function Attrs: noinline nounwind optnone uwtable
define dso_local void @_ZN1AC2Ev(ptr %0) #0 {
  %2 = alloca ptr, i64 1, align 8
  store ptr %0, ptr %2, align 8
  %3 = load ptr, ptr %2, align 8
  ret void
}

define void @_GLOBAL__sub_I_global_alias.cpp() {
  call void @__cxx_global_var_init()
  ret void
}

attributes #0 = { noinline nounwind optnone uwtable }

!llvm.module.flags = !{!0, !1}

!0 = !{i32 7, !"uwtable", i32 2}
!1 = !{i32 2, !"Debug Info Version", i32 3}
Operand is null
  call <cannot get addrspace!> void <null operand!>(ptr @A)
fatal error: error in backend: Lowering from LLVMIR dialect to llvm IR failed!
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.      Program arguments: ./build/bin/clang --target=x86_64-unknown-linux -S scratch/global_alias.cpp -o - --sysroot=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.4.sdk -emit-llvm -fclangir
1.      <eof> parser at end of file
 #0 0x000000010421a278 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x101846278)
 #1 0x0000000104217d60 llvm::sys::RunSignalHandlers() (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x101843d60)
 #2 0x0000000104219824 llvm::sys::CleanupOnSignal(unsigned long) (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x101845824)
 #3 0x0000000104184924 (anonymous namespace)::CrashRecoveryContextImpl::HandleCrash(int, unsigned long) (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x1017b0924)
 #4 0x0000000104184894 llvm::CrashRecoveryContext::HandleExit(int) (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x1017b0894)
 #5 0x0000000104214b84 llvm::sys::Process::Exit(int, bool) (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x101840b84)
 #6 0x00000001029db1b8 llvm::iplist_impl<llvm::simple_ilist<llvm::AliasSet>, llvm::ilist_traits<llvm::AliasSet>>::erase(llvm::ilist_iterator<llvm::ilist_detail::node_options<llvm::AliasSet, true, false, void, false, void>, false, false>) (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x1000071b8)
 #7 0x000000010418bad4 llvm::report_fatal_error(llvm::Twine const&, bool) (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x1017b7ad4)
 #8 0x000000010418b9a0 llvm::report_fatal_error(llvm::Twine const&, bool) (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x1017b79a0)
 #9 0x0000000105244d34 cir::direct::CIRToLLVMPtrStrideOpLowering::~CIRToLLVMPtrStrideOpLowering() (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x102870d34)
#10 0x00000001052142d4 cir::CIRGenConsumer::HandleTranslationUnit(clang::ASTContext&) (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x1028402d4)
#11 0x00000001079ccf98 clang::ParseAST(clang::Sema&, bool, bool) (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x104ff8f98)
#12 0x0000000104e245c4 clang::FrontendAction::Execute() (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x1024505c4)
#13 0x0000000104da1f44 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x1023cdf44)
#14 0x0000000104f160fc clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x1025420fc)
#15 0x00000001029d9ffc cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x100005ffc)
#16 0x00000001029d7dac ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x100003dac)
#17 0x0000000104c451d8 void llvm::function_ref<void ()>::callback_fn<clang::driver::CC1Command::Execute(llvm::ArrayRef<std::__1::optional<llvm::StringRef>>, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>*, bool*) const::$_0>(long) (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x1022711d8)
#18 0x0000000104184848 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x1017b0848)
#19 0x0000000104c447c0 clang::driver::CC1Command::Execute(llvm::ArrayRef<std::__1::optional<llvm::StringRef>>, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>*, bool*) const (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x1022707c0)
#20 0x0000000104c0687c clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x10223287c)
#21 0x0000000104c06a98 clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::__1::pair<int, clang::driver::Command const*>>&, bool) const (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x102232a98)
#22 0x0000000104c25fc0 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::__1::pair<int, clang::driver::Command const*>>&) (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x102251fc0)
#23 0x00000001029d7048 clang_main(int, char**, llvm::ToolContext const&) (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x100003048)
#24 0x00000001029e4c60 main (/Users/jjasmine/Developer/igalia/clangir/build/bin/clang-22+0x100010c60)
#25 0x00000001892f6b98