[llvm-dev] Question about Constant expressions

[Johannes Doerfert via llvm-dev]

Hi James,


Like other constant expressions, e.g., i32 0, this GEP constant

expression are "shown" inlined. Constants are unique and exist

everywhere. I guess the most "important' use case I can think

of is to use such GEPs as part of other constant expressions,

e.g., initializers of constant globals.


Cheers,

   Johannes


On 5/31/20 3:49 AM, James Courtier-Dutton via llvm-dev wrote:
> Hi,
>
> Why is the getelementptr part of the call instruction, instead of
> being a separate instruction in the LLVM IR ?
> The LLVM IR Builder adds it as a separate instruction, but it is
> rolled into one call instruction in the .bc output.
> I am just curious as to why it is done this way.
>
> #include <stdint.h>
> #include <stdio.h>
> int test21(void);
> int test21(void) {
>          printf("Hello1\n");
>          return 0;
> }
>
> define dso_local i32 @test21() #0 {
>    %1 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([8 x
> i8], [8 x i8]* @.str, i64 0, i64 0))
>    ret i32 0
> }
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