Re: question about linker

On 27/11/2024 09:57, Thiago Adams wrote:

On 27/11/2024 09:38, Thiago Adams wrote:

On 27/11/2024 09:10, Bart wrote:

On 27/11/2024 11:57, Bart wrote:

On 27/11/2024 01:52, Thiago Adams wrote:

>

I also use ILs for my compilers, but I write my own backends. I've worked on two diifferent kinds. One looks like a HLL, and only exists for my language. So this original source:

>

  I was wondering if is possible to write C programs without struct/union?
 I did this experiment.
 struct X {
     int a, b;
};
 void F1() {
     struct X x;
     x.a = 1;
     x.b = 2;
     printf("%d, %d", x.a, x.b);
}
 The equivalent C89 program in a subset without structs count be
 #define M(T, obj, OFF) *((T*)(((char*)&(obj)) + (OFF)))
 void F2() {
     char x[8];
     M(int, x, 0 /*offset of a*/) = 1;
     M(int, x, 4 /*offset of b*/) = 2;
     printf("\n");
     printf("%d, %d", M(int, x, 0), M(int, x, 4));
}
 The char array represents the struct X memory, then we  have to find the offset of the members and cast to their types.
  Does your IL have structs?
 The QBE IL has aggregates types. I think this removes the front end calculate the the offsets.
 https://c9x.me/compile/doc/il.html#Aggregate-Types
   

I tried this sample with clang and -S -emit-llvm to see if it generates structs. The answer is yes.
https://llvm.org/docs/LangRef.html#getelementptr-instruction
struct RT {
   char A;
   int B[10][20];
   char C;
};
struct ST {
   int X;
   double Y;
   struct RT Z;
};
int *foo(struct ST *s) {
   return &s[1].Z.B[5][13];
}
The LLVM code generated by Clang is approximately:
%struct.RT = type { i8, [10 x [20 x i32]], i8 }
%struct.ST = type { i32, double, %struct.RT }
define ptr @foo(ptr %s) {
entry:
   %arrayidx = getelementptr inbounds %struct.ST, ptr %s, i64 1, i32 2, i32 1, i64 5, i64 13
   ret ptr %arrayidx
}
It is not much different than C in this aspect.