From b81854e34e444042c454abaef3684d1c1d32eae4 Mon Sep 17 00:00:00 2001
From: Martin Kinkelin <mkinkelin@symmetryinvestments.com>
Date: Thu, 7 Sep 2023 16:14:53 +0100
Subject: [PATCH] Lazily IR-declare global variables

Analogous to #4420.
---
 gen/declarations.cpp                          |  7 +++++--
 tests/codegen/avr.d                           |  2 ++
 tests/codegen/wasi.d                          |  2 --
 tests/fail_compilation/global_var_collision.d | 11 ++++++++++-
 4 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/gen/declarations.cpp b/gen/declarations.cpp
index d98652a2ebb..1e51651212b 100644
--- a/gen/declarations.cpp
+++ b/gen/declarations.cpp
@@ -236,9 +236,12 @@ class CodegenVisitor : public Visitor {
                            decl->toPrettyChars());
     LOG_SCOPE;
 
-    if (decl->ir->isDefined()) {
+    if (decl->ir->isDefined())
+      return;
+
+    // skip external declarations (IR-declared lazily)
+    if (decl->storage_class & STCextern)
       return;
-    }
 
     if (decl->type->ty == TY::Terror) {
       decl->error("had semantic errors when compiling");
diff --git a/tests/codegen/avr.d b/tests/codegen/avr.d
index c473cc7dc12..1e0c4073dff 100644
--- a/tests/codegen/avr.d
+++ b/tests/codegen/avr.d
@@ -11,3 +11,5 @@ version (D_SoftFloat) {} else static assert(0);
 int definedGlobal = 123;
 // CHECK: @_D3avr14declaredGlobali = external global i32
 extern int declaredGlobal;
+
+int dummyRef() { return declaredGlobal; } // make sure `declaredGlobal` is IR-declared
diff --git a/tests/codegen/wasi.d b/tests/codegen/wasi.d
index 2e33d5b4e24..28e67ed037a 100644
--- a/tests/codegen/wasi.d
+++ b/tests/codegen/wasi.d
@@ -15,8 +15,6 @@ version (CRuntime_WASI) {} else static assert(0);
 
 // CHECK: @_D4wasi13definedGlobali = global i32 123
 int definedGlobal = 123;
-// CHECK: @_D4wasi14declaredGlobali = external global i32
-extern int declaredGlobal;
 
 
 // make sure the ModuleInfo ref is emitted into the __minfo section:
diff --git a/tests/fail_compilation/global_var_collision.d b/tests/fail_compilation/global_var_collision.d
index 89be7c930be..641131fba98 100644
--- a/tests/fail_compilation/global_var_collision.d
+++ b/tests/fail_compilation/global_var_collision.d
@@ -1,8 +1,17 @@
+// It should compile fine when not referencing the colliding external global:
+// RUN: %ldc -c %s -d-version=DontReference
+
+// But fail if referenced:
 // RUN: not %ldc -c %s 2>&1 | FileCheck %s
 
 extern(C) extern int myGlobal;
 
-// CHECK:      global_var_collision.d(9): Error: Global variable type does not match previous declaration with same mangled name: `myGlobal`
+version (DontReference) {} else
+{
+    int dummyRef() { return myGlobal; }
+}
+
+// CHECK:      global_var_collision.d([[@LINE+4]]): Error: Global variable type does not match previous declaration with same mangled name: `myGlobal`
 // CHECK-NEXT: Previous IR type: i32, mutable, thread-local
 // CHECK-NEXT: New IR type:      i64, const, non-thread-local
 pragma(mangle, myGlobal.mangleof)