Request for discussion: Rewrite of inline assembler docs

[Andrew Haley]

On 03/28/2014 06:20 AM, dw wrote:
> Using this clobber causes the compiler to flush all (modified) registers 
> being used to store memory-based values to memory before executing the 
> @code{asm} statement.

I don't know what a "memory-based" value is.  This phrase doesn't help
at all.  In addition, it isn't true.  Modified registers are not
flushed to memory unless they are clobbered or their address is taken.
This sentence should be deleted.

Andrew.

int sum(int a[], int l) {
  int i;
  int sum = 0;
  for (i = 0; i < l; i++) {
    asm volatile("nop # Nothing at all":::"memory");
    sum += a[i];
  }
  return sum;
}


at -O2:


sum:
.LFB0:
	.cfi_startproc
	xorl	%eax, %eax
	testl	%esi, %esi
	jle	.L3
	subl	$1, %esi
	xorl	%edx, %edx
	leaq	4(,%rsi,4), %rcx
	.p2align 4,,10
	.p2align 3
.L4:
#APP
# 5 "z.c" 1
	nop # Nothing at all
# 0 "" 2
#NO_APP
	addl	(%rdi,%rdx), %eax
	addq	$4, %rdx
	cmpq	%rcx, %rdx
	jne	.L4
.L3:
	rep
	ret