clang -emit-llvm -S -O3 red.c

; Function Attrs: nounwind ssp uwtable
define i32 @main() #0 {
  %1 = tail call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([3 x i8]* @.str, i64 0, i64 0), double 3.500000e+00) #3
  ret i32 0
}

gcc -S -O3 red.c

LCPI0_0:
	.quad	4615063718147915776     ## double 3.5
	.section	__TEXT,__text,regular,pure_instructions
	.globl	_main
	.align	4, 0x90
_main:                                  ## @main
	.cfi_startproc
## BB#0:
	pushq	%rbp
Ltmp2:
	.cfi_def_cfa_offset 16
Ltmp3:
	.cfi_offset %rbp, -16
	movq	%rsp, %rbp
Ltmp4:
	.cfi_def_cfa_register %rbp
	leaq	L_.str(%rip), %rdi
	movsd	LCPI0_0(%rip), %xmm0
	movb	$1, %al
	callq	_printf
	xorl	%eax, %eax
	popq	%rbp
	retq

red.c

#include <stdio.h>
float mid(float a, float b);

int main() {
    printf("%f", mid(2.0, 5.0));
    return 0;
}

float mid(float a, float b) {
    return (a + b)*0.5; 
}