logo
down
shadow

Is there a reason why Clang does not optimize this code?


Is there a reason why Clang does not optimize this code?

By : blueseaaaa
Date : October 18 2020, 06:10 AM
it should still fix some issue The code you've given is way overcomplicated. You can replace it with:
code :
void to_bytes(uint64_t x, uint8_t* dest) {
    x = htole64(x);
    std::memcpy(dest, &x, sizeof(x));
}


Share : facebook icon twitter icon
Show reason for deprecation in Clang

Show reason for deprecation in Clang


By : desdesdes
Date : March 29 2020, 07:55 AM
Any of those help The deprecated attribute is described in N3797 [dcl.attr.deprecated]. The section is short, so I'll include it entire:
7.6.5 Deprecated attribute [dcl.attr.deprecated]
Why does Clang optimize away x * 1.0 but NOT x + 0.0?

Why does Clang optimize away x * 1.0 but NOT x + 0.0?


By : Raphael Rodrigues
Date : March 29 2020, 07:55 AM
help you fix your problem The IEEE 754-2008 Standard for Floating-Point Arithmetic and the ISO/IEC 10967 Language Independent Arithmetic (LIA) Standard, Part 1 answer why this is so.
IEEE 754 § 6.3 The sign bit
Can LTO for gcc or clang optimize across C and C++ methods

Can LTO for gcc or clang optimize across C and C++ methods


By : Elliot Cohen
Date : March 29 2020, 07:55 AM
wish help you to fix your issue Yes!
Link-time optimization typically works on intermediate representation (IR) present in "fat" object files, which can contain both machine code for traditional linking, and IR for LTO linking.
code :
gcc -c -flto foo.c
g++ -c -flto bar.cc
gfortran -c -flto baz.f90
g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran
#ifndef FUNC_DOT_H
#define FUNC_DOT_H

#ifdef __cplusplus
extern "C" {
#endif

int func(int a, int b, int c);

#ifdef __cplusplus
}
#endif

#endif /* FUNC_DOT_H */
#include "func.h"

int func(int a, int b, int c)
{
    return 3*a + 2*b + c;
}
#include "func.h"

int main()
{
    int a = 1;
    int b = 2;
    int c = 3;

    return func(a, b, c);
}
gcc -o func.o -c -Wall -Werror -flto -O2 func.c
g++ -o main.o -c -Wall -Werror -flto -O2 main.cpp
g++ -o testlto -flto -O2 main.o func.o
Disassembly of section .text:

00000000004003d0 <main>:
  4003d0:   b8 0a 00 00 00          mov    eax,0xa   ; 1*3 + 2*2 + 3 = 10
  4003d5:   c3                      ret
00000000004004b0 <main>:
  4004b0:   b8 0a 00 00 00          mov    eax,0xa
  4004b5:   c3                      ret
What is the reason for different performance of the same implementation using icc, gcc and clang?

What is the reason for different performance of the same implementation using icc, gcc and clang?


By : Aayush Jain
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further The different compilers actually use fairly different implementation strategies here.
GCC notices that it never has to re-load a[i-8] which was calculated in the previous iteration and therefore can be sourced from a register. This relies on mov-elimination somewhat, otherwise the reg-reg move would still add some latency, though even without mov-elimination it would be a lot faster than reloading every time.
code :
dep1 = _mm256_load_si256((__m256i *) &a[0]);
for(; i<LEN-1; i+=8){

    dep1 = _mm256_add_epi32(dep1, coeff);
    _mm256_store_si256((__m256i *) &a[i], dep1);    

}
clang: error: clang frontend command failed with exit code 70 (use -v to see invocation)

clang: error: clang frontend command failed with exit code 70 (use -v to see invocation)


By : Amey Temporary
Date : March 29 2020, 07:55 AM
will be helpful for those in need I got this error when i was archiving my app with xcode - while running on sim and physical device worked -, but had my physical device still selected as a scheme. Solution worked for me: clean build folder, and select 'Generic IOS Device' as the scheme.
Related Posts Related Posts :
  • C++ pointer to const pointer
  • Is using macros to abbreviate long winded boost template names a bad practice?
  • How to detect end-of-file when using getline?
  • Converting QXmlItem to QtDomElement or similar?
  • C++ freeing static variables
  • Compiling/Debugging LZMA
  • What is the fastest way to find out the time in the windows with an accuracy of 1ms?
  • Increment order
  • C++0x atomic implementation in c++98 question about __sync_synchronize()
  • C++ - Access array (in main) from methods outside main
  • How can i stream CCTV camera to iphone from windows
  • Function that counts the number of integers in a text file?
  • "Reading" a POD preincrement result does not yield undefined behavior. Why exactly?
  • Can nullptr be emulated in gcc?
  • Swapping one widget with another in Qt
  • Fastest C++ Signal/Slot Lib without dependency
  • Isn't this an error in the book The C++ Programming Language(4 ed)?
  • Error in C++ Vector Usage: No matching member function for call to 'push_back'
  • Can someone tell me why I am unable to find the length of array using sizeof() function here?
  • How to cout a constructor?
  • printf treats *p++ differently from what happens to p
  • How to pass a constexpr array into a function
  • OpenCV building fails due to DirectX
  • How to 'backspace' using a pushbutton
  • Binary literal in condition
  • Access captured variables outside the lambda
  • Storing 4 values from each line from a txt file, into an object - C++
  • What is the most efficient way to test for duplicates in a user inputted array?
  • How to find a string in a binary file?
  • Passing variable into lambda
  • decltype(auto) function return type does not deduce && types
  • Find the unique elements of a vector C++
  • Why doesn't str != "hello" && "goodbye" work?
  • Array rotate and delete
  • Is the concept of release-sequence useful in practice?
  • Multiple spotlights in opengl doesn't work
  • The for loop isn't entered even if the initial requirement is true
  • Function is called twice from the same thread for the same object with the same call stack
  • Filling char pointer correctly
  • How Base class members gets copied in inheritance when we copy/assign derived class objects?
  • call method from a function pointer
  • Is it common to declare const pointers in C++?
  • How to check whether new threads created inside third party DLL in visual c++ application
  • I cannot convert a '2D array whit bool' to a 'void 2D array bool'(for game of life)
  • How to send variables between classes in Qt
  • What are the similarities and differences between C++'s concepts and Rust's traits?
  • Variadic templates in C++ 11 and class constructors
  • getting segmentation fault when copying arrays using std::copy
  • std::cout is decreasing CPU Usage?
  • Trying to use find_if function to locate value in vector of pairs by first element
  • Lottery simulator is returning garbage values and not the users lotto numbers and the winning numbers
  • error: expression must have integral or unscoped enum type when incrementally filling in vectors
  • auto fail to deduce correct return type
  • Pass string or wstring in a function
  • Is there a way to get some function called on every thread that gets created?
  • How can I enforce two function parameters have the same template type?
  • Using strcpy_s() and strcat_s() with dynamically allocated strings
  • Tensorflow Lite arm64 error: cannot convert ‘const int8x8_t?
  • How to pass `this` pointer from outer class to a member structure?
  • Storing integers values from file into a vectors of vector
  • shadow
    Privacy Policy - Terms - Contact Us © 35dp-dentalpractice.co.uk