#define NULL ((void *)0)
typedef unsigned long size_t; // Customize by platform.
typedef long intptr_t;
typedef unsigned long uintptr_t;
typedef long scalar_t__; // Either arithmetic or pointer type.
/* By default, we understand bool (as a convenience). */
typedef int bool;
#define false 0
#define true 1

/* Forward declarations */

/* Type definitions */

/* Variables and functions */
int EXIT_SUCCESS;
char *getenv(char *);
int /*<<< orphan*/ printf(char *, char *);
int /*<<< orphan*/ putenv(char *);
int main(int argc, char **argv) {
  printf("user = %s\n", getenv("USER"));
  putenv("USER=test");
  printf("user = %s\n", getenv("USER"));
  return EXIT_SUCCESS;
}


x86 assembly (clang, -O0):
<main>:
push   %rbp
mov    %rsp,%rbp
sub    $0x10,%rsp
movl   $0x0,-0x4(%rbp)
mov    %edi,-0x8(%rbp)
mov    %rsi,-0x10(%rbp)
lea    0xebe(%rip),%rdi
call   1030 <getenv@plt>
mov    %rax,%rsi
lea    0xea4(%rip),%rdi
call   1040 <printf@plt>
lea    0xea8(%rip),%rdi
call   1050 <putenv@plt>
lea    0xe97(%rip),%rdi
call   1030 <getenv@plt>
mov    %rax,%rsi
lea    0xe7d(%rip),%rdi
call   1040 <printf@plt>
mov    0x2e51(%rip),%rax
mov    (%rax),%eax
add    $0x10,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<main>:
push   %r14
push   %rbx
push   %rax
lea    0xed0(%rip),%r14
mov    %r14,%rdi
call   1030 <getenv@plt>
lea    0xeb6(%rip),%rbx
mov    %rbx,%rdi
mov    %rax,%rsi
call   1040 <printf@plt>
lea    0xeb4(%rip),%rdi
call   1050 <putenv@plt>
mov    %r14,%rdi
call   1030 <getenv@plt>
mov    %rbx,%rdi
mov    %rax,%rsi
call   1040 <printf@plt>
mov    0x2e65(%rip),%rax
mov    (%rax),%eax
add    $0x8,%rsp
pop    %rbx
pop    %r14
ret

LLVM IR (-O0):
@.str = [11 x i8] c"user = %s\0A\00"
@.str.1 = [5 x i8] c"USER\00"
@.str.2 = [10 x i8] c"USER=test\00"
@EXIT_SUCCESS = global i32 0
define i32 @main(i32 %0, i8** %1) {
%3 = alloca i32
%4 = alloca i32
%5 = alloca i8**
store i32 0, i32* %3
store i32 %0, i32* %4
store i8** %1, i8*** %5
%6 = call i8* @getenv(i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.1, i64 0, i64 0))
%7 = call i32 @printf(i8* getelementptr inbounds ([11 x i8], [11 x i8]* @.str, i64 0, i64 0), i8* %6)
%8 = call i32 @putenv(i8* getelementptr inbounds ([10 x i8], [10 x i8]* @.str.2, i64 0, i64 0))
%9 = call i8* @getenv(i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.1, i64 0, i64 0))
%10 = call i32 @printf(i8* getelementptr inbounds ([11 x i8], [11 x i8]* @.str, i64 0, i64 0), i8* %9)
%11 = load i32, i32* @EXIT_SUCCESS
ret i32 %11
}

LLVM IR (-O2):
@.str = [11 x i8] c"user = %s\0A\00"
@.str.1 = [5 x i8] c"USER\00"
@.str.2 = [10 x i8] c"USER=test\00"
@EXIT_SUCCESS = global i32 0
define i32 @main(i32 %0, i8** nocapture readnone %1) {
%3 = tail call i8* @getenv(i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.1, i64 0, i64 0))
%4 = tail call i32 @printf(i8* getelementptr inbounds ([11 x i8], [11 x i8]* @.str, i64 0, i64 0), i8* %3)
%5 = tail call i32 @putenv(i8* getelementptr inbounds ([10 x i8], [10 x i8]* @.str.2, i64 0, i64 0))
%6 = tail call i8* @getenv(i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.1, i64 0, i64 0))
%7 = tail call i32 @printf(i8* getelementptr inbounds ([11 x i8], [11 x i8]* @.str, i64 0, i64 0), i8* %6)
%8 = load i32, i32* @EXIT_SUCCESS
ret i32 %8
}