Fix for PR46384. Failure on weak dllimport.

[Sunil_Srivastava]

Summary

The patch simply relaxes the check. I think it is OK to have dllimport-weak-externals.

[wristow]

llvm/lib/IR/Verifier.cpp

593

This relaxation of the assertion-check LGTM.

llvm/test/Verifier/weak-dllimport.ll

1

This test seems somewhat complicated. Can it be simplified significantly, and still trigger the problem?

[Sunil_Srivastava]

llvm/test/Verifier/weak-dllimport.ll

1

Yes it can be simplified. Most of the executable code and attributes can go away. It will lose its connection to the source though. Is that preferred ?

[wristow]

llvm/test/Verifier/weak-dllimport.ll

1

IMO, yes that's preferred.

Leaving a fragment of source in as a comment to show how the situation came about is fine. But simplifying the IR of the test so it focuses on the problem makes it clearer to me.

[Sunil_Srivastava]

Simplified the test case.

[wristow]

In D86907#2250689, @Sunil_Srivastava wrote:

Simplified the test case.

Thanks. The reduced test looks good.

Overall: LGTM.

[Sunil_Srivastava]

Tweaked the test to specifically look for the error of interest

[wristow]

In D86907#2253599, @Sunil_Srivastava wrote:

Tweaked the test to specifically look for the error of interest

LGTM

llvm/lib/IR/Verifier.cpp

void Verifier::visitGlobalValue(const GlobalValue &GV) {
 
   if (GV.isDeclarationForLinker())
     Assert(!GV.hasComdat(), "Declaration may not be in a Comdat!", &GV);
 
   if (GV.hasDLLImportStorageClass()) {
     Assert(!GV.isDSOLocal(),
            "GlobalValue with DLLImport Storage is dso_local!", &GV);
 
-    Assert((GV.isDeclaration() && GV.hasExternalLinkage()) ||
+    Assert((GV.isDeclaration() &&
+            (GV.hasExternalLinkage() || GV.hasExternalWeakLinkage())) ||
                GV.hasAvailableExternallyLinkage(),
            "Global is marked as dllimport, but not external", &GV);
   }
 
   if (GV.isImplicitDSOLocal())
     Assert(GV.isDSOLocal(),
            "GlobalValue with local linkage or non-default "
            "visibility must be dso_local!",

llvm/test/Verifier/weak-dllimport.ll

+; RUN: opt -verify < %s
+; ModuleID = 'wd.cpp'
+source_filename = "wd.cpp"
+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-pc-windows-msvc19.11.0"
+
+@"?var_hook@@3HA" = extern_weak dllimport global i32, align 4
+
+; Function Attrs: noinline optnone uwtable
+define dso_local zeroext i1 @"?foo@@YA_NPEAHH@Z"(i32* %0, i32 %1) #0 {
+  %3 = alloca i32, align 4
+  %4 = alloca i32*, align 8
+  store i32 %1, i32* %3, align 4
+  store i32* %0, i32** %4, align 8
+  br i1 icmp ne (void (i32)* @func_hook, void (i32)* null), label %5, label %7
+
+5:                                                ; preds = %2
+  %6 = load i32, i32* %3, align 4
+  call void @func_hook(i32 %6)
+  br label %7
+
+7:                                                ; preds = %5, %2
+  %8 = load i32*, i32** %4, align 8
+  %9 = icmp eq i32* @"?var_hook@@3HA", %8
+  ret i1 %9
+}
+
+declare extern_weak dllimport void @func_hook(i32) #1
+
+attributes #0 = { noinline optnone uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+
+!llvm.module.flags = !{!0, !1}
+!llvm.ident = !{!2}
+
+!0 = !{i32 1, !"wchar_size", i32 2}
+!1 = !{i32 7, !"PIC Level", i32 2}
+!2 = !{!"clang version 12.0.0 (https://github.com/llvm/llvm-project.git 60db26a66d5346b2feae279f6c928bde48078893)"}
+
+; Compiled from the following C++ example with --target=x86_64-pc-win32, 
+; using the non-checking configuration
+;__declspec(dllimport) __attribute__((
+;    weak)) extern "C" void func_hook(int);
+;extern __declspec(dllimport) __attribute__((weak)) int var_hook;
+;
+;bool foo(int *q, int p)
+;{
+;  if (func_hook)
+;    func_hook(p);
+;  return &var_hook == q;
+;}