Extended Description

LLVM is considering that the if is always true.

test:
extern int test_weak () attribute ((weak));

int main(){
int (*t)() = test_weak;
if (t)
return t();
else return 250;
}

llc emits:
.text
.align 16
.globl main
.type main,@function
main:
subl $4, %esp
fnstcw 2(%esp)
movb $2, 3(%esp)
fldcw 2(%esp)
.LBB1_1: #cond_true
call test_weak
addl $4, %esp
ret
.size main, .-main
.weak test_weak

gcc emits:
.file "teste.c"
.text
.p2align 4,,15
.globl main
.type main, @​function
main:
leal 4(%esp), %ecx
andl $-16, %esp
pushl -4(%ecx)
movl $test_weak, %eax
movl $250, %edx
pushl %ebp
movl %esp, %ebp
pushl %ecx
subl $4, %esp
testl %eax, %eax
je .L4
call test_weak
movl %eax, %edx
.L4:
addl $4, %esp
movl %edx, %eax
popl %ecx
popl %ebp
leal -4(%ecx), %esp
ret
.size main, .-main
.weak test_weak
.ident "GCC: (GNU) 4.1.2 20060928 (prerelease) (Ubuntu 4.1.1-13ubuntu5)"
.section .note.GNU-stack,"",@progbits