[LLD] [COFF] Fix automatically importing data symbols from DLLs with LTO

[mstorsjo]

Summary

This broke in 51dcb292cc002, "[lld-link] diagnose undefined symbols before LTO when possible" (very soon after the 9.0 branch, so luckily the 9.0 release is unaffected).

The code for loading objects we believe might be needed for autoimport (loadMinGWAutomaticImports()) does run before the new reportUnresolvable() function, but it had a condition to only operate on symbols from regular object files. This condition came from resolveRemainingUndefines(), but as loadMinGWAutomaticImports() now has to operate before the LTO, it has to operate on undefineds from LTO objects as well.

[rnk]

lgtm

lld/COFF/SymbolTable.cpp

 }
 
 void SymbolTable::loadMinGWAutomaticImports() {
   for (auto &i : symMap) {
     Symbol *sym = i.second;
     auto *undef = dyn_cast<Undefined>(sym);
     if (!undef)
       continue;
-    if (!sym->isUsedInRegularObj)
-      continue;
     if (undef->getWeakAlias())
       continue;
 
     StringRef name = undef->getName();
 
     if (name.startswith("__imp_"))
       continue;
     // If we have an undefined symbol, but we have a lazy symbol we could

lld/test/COFF/autoimport-lto.ll

+; REQUIRES: x86
+
+; RUN: echo -e ".global variable\n.global DllMainCRTStartup\n.text\nDllMainCRTStartup:\nret\n.data\nvariable:\n.long 42" > %t-lib.s
+; RUN: llvm-mc -triple=x86_64-windows-gnu %t-lib.s -filetype=obj -o %t-lib.obj
+; RUN: lld-link -out:%t-lib.dll -dll -entry:DllMainCRTStartup %t-lib.obj -lldmingw -implib:%t-lib.lib
+
+; RUN: llvm-as -o %t.obj %s
+; RUN: lld-link -lldmingw -out:%t.exe -entry:entry %t.obj %t-lib.lib
+
+; RUN: llvm-readobj --coff-imports %t.exe | FileCheck -check-prefix=IMPORTS %s
+
+; IMPORTS: Import {
+; IMPORTS-NEXT: Name: autoimport-lto.ll.tmp-lib.dll
+; IMPORTS-NEXT: ImportLookupTableRVA:
+; IMPORTS-NEXT: ImportAddressTableRVA:
+; IMPORTS-NEXT: Symbol: variable (0)
+; IMPORTS-NEXT: }
+
+target datalayout = "e-m:w-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-w64-windows-gnu"
+
+@variable = external global i32
+
+define i32 @entry() {
+entry:
+  %0 = load i32, i32* @variable
+  ret i32 %0
+}