From bd6148dd6b77920cf64fea8804b205e8257e8a66 Mon Sep 17 00:00:00 2001 From: Jesse Meyer Date: Tue, 3 Feb 2026 20:16:44 -0500 Subject: Fix Windows LTO: preserve required procedures with llvm.used On Windows with LTO, required procedures with external linkage need to be added to @llvm.used to survive linker-level dead code elimination. LLVM may generate implicit calls to runtime builtins (e.g., __extendhfsf2 for f16 conversions) during instruction lowering, after the IR is finalized. Without @llvm.used, the linker discards these procedures before the implicit calls are generated. This adds required procedures to @llvm.used at creation time. The fix is Windows-specific; other platforms handle this correctly. Co-Authored-By: Claude Opus 4.5 --- src/llvm_backend_proc.cpp | 13 +++++++++++++ 1 file changed, 13 insertions(+) (limited to 'src/llvm_backend_proc.cpp') diff --git a/src/llvm_backend_proc.cpp b/src/llvm_backend_proc.cpp index 837d7ce48..cb8ffcf91 100644 --- a/src/llvm_backend_proc.cpp +++ b/src/llvm_backend_proc.cpp @@ -289,6 +289,19 @@ gb_internal lbProcedure *lb_create_procedure(lbModule *m, Entity *entity, bool i lb_set_linkage_from_entity_flags(p->module, p->value, entity->flags); + // With LTO on Windows, required procedures with external linkage need to be added to + // llvm.used to survive linker-level dead code elimination. This is necessary because + // LLVM may generate implicit calls to runtime builtins (e.g., __extendhfsf2 for f16 + // conversions) during instruction lowering, after the IR is finalized. + if (build_context.lto_kind != LTO_None && build_context.metrics.os == TargetOs_windows) { + if (entity->flags & EntityFlag_Require) { + LLVMLinkage linkage = LLVMGetLinkage(p->value); + if (linkage != LLVMInternalLinkage) { + lb_append_to_used(m, p->value); + } + } + } + if (m->debug_builder) { // Debug Information Type *bt = base_type(p->type); -- cgit v1.2.3