All Questions
Tagged with compiler-flags compiler-optimization
18 questions
1
vote
1
answer
286
views
Improve g++ compiler flags for debug and release
I am making a game in c++ with sdl2, and I am currently compiling the program with g++ using the following flags:
DEBUG_FLAGS = -g -Og -DDEBUG
RELEASE_FLAGS = -O3 -DNDEBUG -mwindows -s
I want the ...
- 52
0
votes
0
answers
58
views
Function inlined in the header increments the wrong attribute: subtle bug
The setup (source files are listed at the bottom). There is a Counters class with 2 counter members and 2 methods to increment them and a 3rd extra #ifndef NDEBUG-guarded "debug" counter and ...
- 897
0
votes
0
answers
232
views
In GCC, how to convert a predefined optimization level into a list of finer grained optimization flags?
I'm measuring how optimization flag number affects the coverage of GCC when it is compiling some test cases. I know GCC has predefined optimization levels, such as -O1 and -O2. I also know how to ...
- 339
2
votes
1
answer
2k
views
Recommendation for nvfortran compiler useful flags
I use gfortran for years but quite new to nvfortran. I would like to ask if anyone can give me recommendation for nvfortran compiler useful flags for both debug and build modes?
what I know for debug ...
- 21
0
votes
0
answers
203
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Force gcc to put all code between prologue and epilogue
When I create very simple C function, something along these lines
void foo(int a) {
for (int i=0; i < a; i++) {
if (i < 4) {
do_something()
} else {
do_something_else()
...
- 673
3
votes
1
answer
1k
views
what are the compilation flags that are activated by using O3
we are in the process of changing the intel compiler version from v14 to v18 in our systems and by running the tests, we have noticed that O3 in some cases produces incorrect results whereas the same ...
- 156
0
votes
1
answer
86
views
GCC flag to ignore instruction dependencies
I am trying to decompile a piece of code and apparently gcc prefers less complicated instructions over the more complex ones. After reading this answer I suspect it's because gcc is trying to reduce ...
- 833
0
votes
2
answers
622
views
g++ -fno-enforce-eh-specs - why/how does this violate the C++ standard?
From man gcc:
-fno-enforce-eh-specs
Don't generate code to check for violation of exception specifications
at run time. This option violates the C++ standard, but may be useful
...
- 130k
23
votes
1
answer
11k
views
What flags does -march=native activate with Clang?
With GCC one is able to print out the specific flags that -march=native triggers. Is it possible to have Clang print similar information?
2
votes
3
answers
257
views
How can I compile this very big, but boring C source?
The central function in my code looks like this (everything else is vanilla input and output):
const int n = 40000;
double * foo (double const * const x)
{
double * y = malloc (n*sizeof(double));...
- 4,375
5
votes
3
answers
3k
views
Is it realistic to use -O3 or -Ofast to compile your benchmark code or will it remove code?
When compiling the benchmark code below with -O3 I was impressed by the difference it made in latency so i began to wonder whether the compiler is not "cheating" by removing code somehow. Is there a ...
- 337
0
votes
1
answer
622
views
Which gcc O2 flag may cause failure in fp calculation?
I compiled paranoia floating point test suit on a pc386 system using GCC O2 level of optimization and got several failures but then compiled it without optimization with the same GCC and got correct ...
9
votes
3
answers
14k
views
What is the proper architecture-specific options (-m) for Sandy Bridge based Pentium?
I'm trying to figure out how to set -march option properly to see how much performance difference between the option enabled and disabled can occur on my PC with gcc 4.7.2.
Before trying compiling, ...
- 509
10
votes
1
answer
4k
views
When to use certain optimizations such as -fwhole-program and -fprofile-generate with several shared libraries
Probably a simple answer; I get quite confused with the language used in the GCC documentation for some of these flags!
Anyway, I have three libraries and a program which uses all these three. I ...
- 183
1
vote
1
answer
366
views
compile with no optimization? as safe as possible?
I have some code acting very weird. Weird enough people accused my output isn't really happening (i wish, that would make my life easier). The code works fine in windows (ms vc++, gcc) but fails on ...
user34537
12
votes
2
answers
3k
views
How much should I optimize?
In regards to optimizations done by the compiler (GCC), what is the standard practice? What does each option (-O, -O1, -O2, -O3, -Os, -s, -fexpensive-optimizations) do differently, and how do I decide ...
user768417
2
votes
2
answers
371
views
Compiler flags change code behavior (O2, Ox)
The following code works as expected with flags Od, O1 but fails with O2, Ox. Any ideas why?
edit: by "fails" I mean that the function does nothing, and seems to just return.
void thread_sleep()
{
...
- 7,145
208
votes
6
answers
131k
views
How to see which flags -march=native will activate?
I'm compiling my C++ app using GCC 4.3. Instead of manually selecting the optimization flags I'm using -march=native, which in theory should add all optimization flags applicable to the hardware I'm ...
- 134k