| Summary: | [OpenMP & C++0x]: Compiler error when lambda-function within OpenMP loop | ||
|---|---|---|---|
| Product: | gcc | Reporter: | Joel Yliluoma <bisqwit> |
| Component: | c++ | Assignee: | Jakub Jelinek <jakub> |
| Status: | RESOLVED FIXED | ||
| Severity: | normal | CC: | jakub |
| Priority: | P3 | ||
| Version: | 4.6.1 | ||
| Target Milestone: | --- | ||
| Host: | Target: | ||
| Build: | Known to work: | ||
| Known to fail: | Last reconfirmed: | 2011-05-19 08:55:08 | |
| Attachments: | gcc46-pr49043.patch | ||
It also happens if the lambda-function does not explicitly contain the "return" statement.
For example, this code triggers the same error.
int main()
{
#pragma omp parallel for
for(int a=0; a<10; ++a)
{
auto func = [] () -> void { };
func();
}
}
Even if the lambda function is not called, it happens. Merely defining the function causes it.
Interestingly though, it does not happen if a method body is defined within the loop. The code below does not cause the error. So it is restricted to lambda function bodies.
It also does not happen when calling lambda functions that are defined outside the loop.
int main()
{
#pragma omp parallel for
for(int a=0; a<10; ++a)
{
struct tmp
{
static int test() { return 0; }
};
}
}
Created attachment 24287 [details] gcc46-pr49043.patch Untested fix. That said, I'd advise not to use lambdas in OpenMP regions, because the OpenMP standard doesn't say anything about the data environment of those and how it should behave. Even the upcoming OpenMP 3.1 doesn't cover C++0x, I hope OpenMP 4.0 will. Author: jakub Date: Thu May 19 13:11:56 2011 New Revision: 173907 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=173907 Log: PR c++/49043 * decl.c (check_omp_return): Stop searching on sk_function_parms. * testsuite/libgomp.c++/pr49043.C: New test. Added: trunk/libgomp/testsuite/libgomp.c++/pr49043.C Modified: trunk/gcc/cp/ChangeLog trunk/gcc/cp/decl.c trunk/libgomp/ChangeLog Author: jakub Date: Thu May 19 13:13:57 2011 New Revision: 173908 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=173908 Log: PR c++/49043 * decl.c (check_omp_return): Stop searching on sk_function_parms. * testsuite/libgomp.c++/pr49043.C: New test. Added: branches/gcc-4_6-branch/libgomp/testsuite/libgomp.c++/pr49043.C Modified: branches/gcc-4_6-branch/gcc/cp/ChangeLog branches/gcc-4_6-branch/gcc/cp/decl.c branches/gcc-4_6-branch/libgomp/ChangeLog Fixed. |
GCC incorrectly considers return statements within lambda functions as "exits" from an OpenMP structured block. For the code below, this error message is generated: tmp3.cc: In lambda function: tmp3.cc:7:40: error: invalid exit from OpenMP structured block #include <iostream> int main() { #pragma omp parallel for for(int a=0; a<10; ++a) { auto func = [=] () { return a; }; std::cout << func(); } } Compiled with: -fopenmp -std=gnu++0x Tested versions: 4.5.3 , 4.6.1 The purpose of this error is to catch exits from an OpenMP construct (return, break, goto). No such thing happens when a lamdba function is called, which is not different from calling an inlined function, therefore the error message is misplaced.