[llvm-dev] Wrong Users count for global string in clang/test/CodeGen/2009-02-13-zerosize-union-field.c

[Craig Topper via llvm-dev]

Each call appears to use an identical ConstantExpr getelementptr. Each of
those ConstantExprs is represented by the same object in the memory
representation of IR even though its printed in 4 separate places. If you
walk the users of that object you should find the 4 calls.

~Craig


On Thu, Nov 26, 2020 at 5:26 PM Nimrod Partush via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi,
>
> I'm writing some code transformations using CLang. When I run my code on clang/test/CodeGen/2009-02-13-zerosize-union-field.c
> :
>
> typedef unsigned int Foo __attribute__((aligned(32)));
> typedef union{Foo:0;}a;
> typedef union{int x; Foo:0;}b;
> extern int printf(const char*, ...);
> int main() {
>   // CHECK: getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i32 0, i32
> 0), i32 0
>   printf("%ld\n", sizeof(a));
>   // CHECK: getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i32 0, i32
> 0), i32 1
>   printf("%ld\n", __alignof__(a));
>   // CHECK: getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i32 0, i32
> 0), i32 4
>   printf("%ld\n", sizeof(b));
>   // CHECK: getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i32 0, i32
> 0), i32 4
>   printf("%ld\n", __alignof__(b));
> }
>
> I see that when I iterate the users() of the "%ld\n" string, only the
> last user is reported. Here's my code for doing the iteration:
>
> for (llvm::GlobalVariable &Glob : TheModule.globals())
>   for (User *U : Glob.users())
>     outs() << "User " << *U << "\n";
>
> The 4 different calls are clearly visible in the .ll file:
>
>   %call = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([5 x
> i8], [5 x i8]* @"??_C at _04PEDNGLFL@?$CFld?6?$AA@", i64 0, i64 0), i64 4)
>   %call1 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([5 x
> i8], [5 x i8]* @"??_C at _04PEDNGLFL@?$CFld?6?$AA@", i64 0, i64 0), i64 1)
>   %call2 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([5 x
> i8], [5 x i8]* @"??_C at _04PEDNGLFL@?$CFld?6?$AA@", i64 0, i64 0), i64 4)
>   %call3 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([5 x
> i8], [5 x i8]* @"??_C at _04PEDNGLFL@?$CFld?6?$AA@", i64 0, i64 0), i64 4)
>
> Any idea why this is happening?
>
> Thanks
>
> --Nimrod.
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