[CIR][CIRGen][TBAA] Struct with Union crashes during CodeGen

[bruteforceboy]

The following code snippet crashes when generating CIR with -O2 enabled after PR#1220 was merged.

typedef struct {
  union {
    int a, b;
  };
  int c;
} S;

void foo(S *s) { s->a = 1; }

I haven't done a thorough review of the changes made, but I just noticed the PR broke something that worked for me before. Can't we add unions here, or just emit tbaa_NYI for all the non-scalar types for now?

cc: @PikachuHyA, @bcardosolopes

[PikachuHyA]

hi @bruteforceboy

Thank you for bringing this to my attention. I sincerely apologize for the issues caused by my recent patch #1220 .

You're correct that the changes affected the handling of unions, leading to the crash you experienced. I've fixed in #1250 .

Thanks again for your feedback, and please let me know if you encounter any further problems or have additional suggestions.

[bruteforceboy]

Hi @PikachuHyA! thanks alot for fixing it, I will test the patch soon. It wasn't a serious issue by the way 😅 I was just bringing it to your attention.

[PikachuHyA]

Can't we add unions here, or just emit tbaa_NYI for all the non-scalar types for now?

follow the skeleton of OG, the union is marked as omnipotent char now

run ./bin/clang t.c -O1 -Xclang -emit-llvm -o t.orig.ll -c

; ModuleID = 't.c'
source_filename = "t.c"
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: write) uwtable
define dso_local void @foo(ptr nocapture noundef writeonly initializes((0, 4)) %s) local_unnamed_addr #0 {
entry:
  store i32 1, ptr %s, align 4, !tbaa !5
  ret void
}

attributes #0 = { mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: write) uwtable "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }

!llvm.module.flags = !{!0, !1, !2, !3}
!llvm.ident = !{!4}

!0 = !{i32 1, !"wchar_size", i32 4}
!1 = !{i32 8, !"PIC Level", i32 2}
!2 = !{i32 7, !"PIE Level", i32 2}
!3 = !{i32 7, !"uwtable", i32 2}
!4 = !{!"clang version 20.0.0git"}
!5 = !{!6, !6, i64 0}
!6 = !{!"omnipotent char", !7, i64 0}
!7 = !{!"Simple C/C++ TBAA"}

run ./bin/clang t.c -O1 -Xclang -emit-llvm -o t.ll -c -fclangir with #1250

; ModuleID = '/disk8/shuoshu.yh/admin_debug/acc_clangir_github/build/t.c'
source_filename = "/disk8/shuoshu.yh/admin_debug/acc_clangir_github/build/t.c"
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: write) uwtable
define dso_local void @foo(ptr nocapture writeonly initializes((0, 4)) %0) local_unnamed_addr #0 {
  store i32 1, ptr %0, align 4, !tbaa !2
  ret void
}

attributes #0 = { mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: write) uwtable }

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

!0 = !{i32 2, !"Debug Info Version", i32 3}
!1 = !{i32 7, !"uwtable", i32 2}
!2 = !{!3, !3, i64 0}
!3 = !{!"omnipotent char", !4, i64 0}
!4 = !{!"Simple C/C++ TBAA"}

[bcardosolopes]

@PikachuHyA that has been my point about crashing valid code, TBAA should be added incrementally without causing churn :)

I'll revert #1220 for now, thanks for the report.

[bcardosolopes]

I had to revert both 1220 and 1242. @PikachuHyA I suggest you don't re-add 1242 until we fix the long long problem, because it might be a bit off depending on what we decide (thanks for working on that though, pretty cool tablegen solution). I suggest you put a new PR for 1220 with the minimum necessary part of #1250 to fix the problem, so we can reland faster.