如何让gfortran或ifort告诉我何时隐含地将REAL（4）推广到REAL（8）？ [英] How can I make gfortran or ifort tell me when it implicitly promotes a REAL(4) to a REAL(8)?

问题描述

我的任务是改变HPC应用程序部件的精度，同时铭记它严重依赖于自动矢量化。因此，编译器告诉我何时发生任何类型的浮点转换转换（因为这可能会对性能造成严重影响）。

<$ c
$ b

-Wconversion 标志听起来像它应该适合我的需要：

Wconversion

警告不同类型之间的隐式转换。

---

https://gcc.gnu.org/onlinedocs/gcc-4.1.0/gfortran/Warning-Options.html

然而，实际上，gfortran 5.2.0似乎只报告浮点降级，例如 REAL（8） 到 REAL（4）。

GCC的 -Wouble-promotion 标志 - 正是我需要的，但不适用于gfortran。 （ https://gcc.gnu.org/onlinedocs/gcc/Warning-Options。 html ）

我正在使用gfortran进行开发，但ifort可用于我。然而，我找不到任何类似的参数 -warn （ https://software.intel.com/zh-cn/node/525184 ）。

我怎样才能得到这些编译器在隐式提升REAL时发出警告？解析方案

您可以参考使用gfortran 5.2.0，所以让我们来看看该版本的文档而不是4.1.0。这有两个相关的标志：




-Wconversion

关于隐式转换的警告转换后很可能会改变表达式的值。隐含的-Wall。

-Wconversion-extra

警告不同类型和种类之间的隐式转换。这个选项并不意味着-Wconversion。


如果我在后面的程序中使用后面的标志

  use，intrinsic :: iso_fortran_env，only：real32，real64 
 real（real64）x 
x = 1._real32 
 end 
  

我在问题标题

中准确地（但使用gfortran 4.8.1） （b）
$ b

$ b

而只是 -Wconversion 我什么都没有。但是，如果我稍微改变了程序，那么为了改变可表示的值，我得到了不同的警告。

I am tasked with changing the precision of parts of an HPC application, bearing in mind that it makes heavy reliance on auto-vectorisation. It is therefore useful for the compiler to inform me when conversions of any type of floating point conversion occurs (as this could have a serious performance impact).

The -Wconversion flag sounds like it should suit my needs:

-Wconversion

Warn about implicit conversions between different types.

---

https://gcc.gnu.org/onlinedocs/gcc-4.1.0/gfortran/Warning-Options.html

However, in practice, gfortran 5.2.0 only appears to report floating point demotions, e.g. REAL(8) to REAL(4).

GCC has the -Wdouble-promotion flag - exactly what I need, but not available for gfortran. (https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html)

I am developing with gfortran, but ifort is available to me. However, I can't find any similar arguments for -warn (https://software.intel.com/en-us/node/525184).

How can I get either of these compilers to emit a warning when implicitly promoting a REAL?

解决方案

You refer to using gfortran 5.2.0, so let's look at the documentation for that version rather than 4.1.0. This has two relevant flags for what you consider:

-Wconversion
Warn about implicit conversions that are likely to change the value of the expression after conversion. Implied by -Wall.
-Wconversion-extra
Warn about implicit conversions between different types and kinds. This option does not imply -Wconversion.

If I use this latter flag with the following program

use, intrinsic :: iso_fortran_env, only : real32, real64
real(real64) x
x = 1._real32
end

I get exactly (albeit using gfortran 4.8.1) a warning message requested in the question title

Warning: Conversion from REAL(4) to REAL(8) at (1)

whereas with just -Wconversion I get nothing. If I change the program slightly, however, so that the changing of representable values kicks in, I get (different) warnings with each.

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