什么是特定的GCC标志，为内联汇编参数打开即时值传播？(What is the specific GCC flag that turns on immediate value propagation

什么是特定的GCC标志，为内联汇编参数打开即时值传播？(What is the specific GCC flag that turns on immediate value propagation for inline assembly parameters?)

考虑下面的x86代码示例：

#include <stdlib.h> static int i; static inline __attribute__((always_inline)) test(int x) { asm volatile("mov %1, %0" : "=r"(i): "i"(x)); } int main(void) { test(5); return i; }

如果我用以下方式构建它：

gcc -O test.c

它建立得很好。

如果我用它构建它（没有优化）：

gcc test.c

它在汇编阶段失败，因为值'5'不会作为内联函数测试的立即值传播，所以我们失败了约束。

我希望能够编译此代码而无需启用其他非相关优化，以便更轻松地进行调试。

从理论上讲， -O只是一个捷径，可以同时启用一堆GCC优化选项，这在GCC手册中有详细介绍 。 不幸的是，我无法找到能够改变这种行为的特定GCC标志。

有任何想法吗？

澄清 ：为了解决任何疑问，代码片段仅仅是一个例子。 除了展示我想要做的事之外，它本身并没有什么意义。 实际的用例涉及到一个自定义处理器的指令，它只能立即作为我试图用C构造包装的参数。 一个宏确实可以做到这一点，但是却忍受着宏的所有常见缺陷，因此我试图避免它。

更新 ：对于那些想知道的人，一个宏也不会工作。 看起来内联函数根本不起作用。 例如，这也不起作用：

void foo (void) { int i = 6; asm volatile ("" : : "i" (i)); }

我还修正了问题标题以反映这一点。

Consider the following x86 code example:

#include <stdlib.h> static int i; static inline __attribute__((always_inline)) test(int x) { asm volatile("mov %1, %0" : "=r"(i): "i"(x)); } int main(void) { test(5); return i; }

If I build it with:

gcc -O test.c

It builds fine.

If I build it with (no optimization):

gcc test.c

It fails during assembly phase, because the value '5' is not propagated as an immediate value to the inline function test, so we fail the constraint.

I wish to be able to compile this code without turning on other non related optimization, in order to make debugging easier.

In theory, -O is simply a short cut to enable a bunch of GCC optimization options at once that are documented in the fine GCC manual. Unfortunately, I was not able to find the specific GCC flag that turns this behavior on.

Any ideas?

Clarification: To relieve any doubt, the code snippet is just an example. It does not make much sense by itself except to show what I am trying to do. The actual use case involves an instruction on a custom processor that can only take an immediate as an argument which I am trying to wrap in a C construct. A macro will indeed do the trick, but suffers from all the usual draw backs of a macro, hence I am trying to avoid it.

Update: For those who wondered, a macro wont work either. It seems the inline function doesn't play a part here at all. E.g., this doesn't work either:

void foo (void) { int i = 6; asm volatile ("" : : "i" (i)); }

I also fixed the question title to reflect this.

最满意答案

看起来像-ftree-ter （替换-ftree-ter >正常传递中的临时表达式 - 不管那是什么）是否-ftree-ter ：

gcc -ftree-ter test.c # no errors

这是我如何确定的：

gcc -Q --help=optimizers告诉您默认启用/禁用哪些优化（某些已启用） gcc -O -Q --help=optimizers告诉你为-O启用/禁用了哪些优化 将这些命令的输出重定向到文件并进行区分。 尝试仅在指定-O时才启用的优化，直到一个工作。

Looks like -ftree-ter (Replace temporary expressions in the SSA->normal pass - whatever that is) does the trick:

gcc -ftree-ter test.c # no errors

Here's how I determined that:

gcc -Q --help=optimizers tells you what optimizations are enabled/disabled by default (some are enabled) gcc -O -Q --help=optimizers tells you what optimizations are enabled/disabled for -O redirect the output of those commands to files and diff them. try the optimizations that are enabled only when -O is specified until one works.