I don't get this C/C++ Joke

Question

After reading this article on thedailywtf.com, I\'m not sure that I really got the joke.

It says there that some guy changed the code from

int function()         


        

Answer 1

I can't get different behavior out of this. I tried it with LLVM: I had to add just a little bit of cruft at the return value so that LLVM doesn't optimize anything away, but the generated code for wtf and wtf2 are totally identical. This wtf is BAAAAAD

Input

#include 
#include 
#include 
int wtf(int X) {
  int x;
  char data_string[15];
  x = 2;
  strcpy(data_string,"data data data");
  return 5*X+x+ data_string[X];
}
int wtf2(int X) {
  int x = 2;
  char data_string[15]="data data data";
  return 5*X+x+ data_string[X];
}
int main(int argc, char **argv) {
  printf("%d\n", wtf(atoi(argv[1]))+wtf2(atoi(argv[1])));
}

Output:

; ModuleID = '/tmp/webcompile/_3856_0.bc'
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32"
target triple = "i386-pc-linux-gnu"
@.str = internal constant [15 x i8] c"data data data\00"        ; <[15 x i8]*> [#uses=3]
@.str1 = internal constant [4 x i8] c"%d\0A\00"     ; <[4 x i8]*> [#uses=1]

define i32 @wtf(i32 %X) nounwind readnone {
entry:
    %0 = mul i32 %X, 5      ;  [#uses=1]
    %1 = getelementptr [15 x i8]* @.str, i32 0, i32 %X      ;  [#uses=1]
    %2 = load i8* %1, align 1       ;  [#uses=1]
    %3 = sext i8 %2 to i32      ;  [#uses=1]
    %4 = add i32 %0, 2      ;  [#uses=1]
    %5 = add i32 %4, %3     ;  [#uses=1]
    ret i32 %5
}

define i32 @wtf2(i32 %X) nounwind readnone {
entry:
    %0 = mul i32 %X, 5      ;  [#uses=1]
    %1 = getelementptr [15 x i8]* @.str, i32 0, i32 %X      ;  [#uses=1]
    %2 = load i8* %1, align 1       ;  [#uses=1]
    %3 = sext i8 %2 to i32      ;  [#uses=1]
    %4 = add i32 %0, 2      ;  [#uses=1]
    %5 = add i32 %4, %3     ;  [#uses=1]
    ret i32 %5
}

define i32 @main(i32 %argc, i8** nocapture %argv) nounwind {
entry:
    %0 = getelementptr i8** %argv, i32 1        ;  [#uses=1]
    %1 = load i8** %0, align 4      ;  [#uses=1]
    %2 = tail call i32 @atoi(i8* %1) nounwind readonly      ;  [#uses=2]
    %3 = getelementptr [15 x i8]* @.str, i32 0, i32 %2      ;  [#uses=1]
    %4 = load i8* %3, align 1       ;  [#uses=1]
    %5 = sext i8 %4 to i32      ;  [#uses=1]
    %tmp2 = mul i32 %2, 10      ;  [#uses=1]
    %6 = shl i32 %5, 1      ;  [#uses=1]
    %7 = add i32 %6, 4      ;  [#uses=1]
    %8 = add i32 %7, %tmp2      ;  [#uses=1]
    %9 = tail call i32 (i8*, ...)* @printf(i8* noalias getelementptr ([4 x i8]* @.str1, i32 0, i32 0), i32 %8) nounwind     ;  [#uses=0]
    ret i32 undef
}

declare i32 @atoi(i8*) nounwind readonly

declare i32 @printf(i8*, ...) nounwind