Long vs int on x64 compile with clang -march=native -O0 -std=c11 test##.c -S -o test##.asm

test.asm.patch

--- test32.asm	2019-03-22 21:28:05.000000000 -0300
+++ test64.asm	2019-03-22 21:28:28.000000000 -0300
@@ -11,11 +11,10 @@
 	movq	%rsp, %rbp
 	.cfi_def_cfa_register %rbp
 	movq	%rdi, -8(%rbp)
-	movl	%esi, -12(%rbp)
-	movq	-8(%rbp), %rdi
-	movl	-12(%rbp), %esi
-	movl	%esi, %eax
-	vcvttsd2si	(%rdi,%rax,8), %eax
+	movq	%rsi, -16(%rbp)
+	movq	-8(%rbp), %rsi
+	movq	-16(%rbp), %rdi
+	vcvttsd2si	(%rsi,%rdi,8), %eax
 	popq	%rbp
 	retq
 	.cfi_endproc

test32.asm

	.section	__TEXT,__text,regular,pure_instructions
	.build_version macos, 10, 14
	.globl	_getElement             ## -- Begin function getElement
	.p2align	4, 0x90
_getElement:                            ## @getElement
	.cfi_startproc
## %bb.0:
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset %rbp, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register %rbp
	movq	%rdi, -8(%rbp)
	movl	%esi, -12(%rbp)
	movq	-8(%rbp), %rdi
	movl	-12(%rbp), %esi
	movl	%esi, %eax
	vcvttsd2si	(%rdi,%rax,8), %eax
	popq	%rbp
	retq
	.cfi_endproc
                                        ## -- End function

.subsections_via_symbols

test32.c

#include <stdio.h>
#include <stdlib.h>
#include <inttypes.h>


#define MYINT uint32_t
#define MYINTScan "%"SCNu32


double getElement(double* array, MYINT index){
	return array[index];
}

test64.asm

	.section	__TEXT,__text,regular,pure_instructions
	.build_version macos, 10, 14
	.globl	_getElement             ## -- Begin function getElement
	.p2align	4, 0x90
_getElement:                            ## @getElement
	.cfi_startproc
## %bb.0:
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset %rbp, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register %rbp
	movq	%rdi, -8(%rbp)
	movq	%rsi, -16(%rbp)
	movq	-8(%rbp), %rsi
	movq	-16(%rbp), %rdi
	vcvttsd2si	(%rsi,%rdi,8), %eax
	popq	%rbp
	retq
	.cfi_endproc
                                        ## -- End function

.subsections_via_symbols

test64.c

#include <stdio.h>
#include <stdlib.h>
#include <inttypes.h>


#define MYINT uint64_t
#define MYINTScan "%"SCNu64


double getElement(double* array, MYINT index){
	return array[index];
}