| Issue |
183613
|
| Summary |
[Clang][OpenMP] Long / indefinite compile times on unexpected OpenMP clause
|
| Labels |
clang
|
| Assignees |
|
| Reporter |
Thyre
|
Godbolt: https://godbolt.org/z/YjGnETc89
---
Some, as far as I know unimplemented, constructs from OpenMP 6.0 cause the following error to appear:
```
clang: warning: argument unused during compilation: '-c' [-Wunused-command-line-argument]
<source>:15:47: error: unexpected OpenMP clause 'induction' in directive '#pragma omp parallel for'
15 | #pragma omp parallel for reduction(+: result) induction(step(x),*: xi)
| ^
<source>:15:47: error: unexpected OpenMP clause 'induction' in directive '#pragma omp parallel for'
<source>:15:47: error: unexpected OpenMP clause 'induction' in directive '#pragma omp parallel for'
<source>:15:47: error: unexpected OpenMP clause 'induction' in directive '#pragma omp parallel for'
<source>:15:47: error: unexpected OpenMP clause 'induction' in directive '#pragma omp parallel for'
<source>:15:47: error: unexpected OpenMP clause 'induction' in directive '#pragma omp parallel for'
<source>:15:47: error: unexpected OpenMP clause 'induction' in directive '#pragma omp parallel for'
<source>:15:47: error: unexpected OpenMP clause 'induction' in directive '#pragma omp parallel for'
<source>:15:47: error: unexpected OpenMP clause 'induction' in directive '#pragma omp parallel for'
<source>:15:47: error: unexpected OpenMP clause 'induction' in directive '#pragma omp parallel for'
<source>:15:47: error: unexpected OpenMP clause 'induction' in directive '#pragma omp parallel for'
<source>:15:47: error: unexpected OpenMP clause 'induction' in directive '#pragma omp parallel for'
<source>:15:47: error: unexpected OpenMP clause 'induction' in directive '#pragma omp parallel for'
<source>:15:47: error: unexpected OpenMP clause 'induction' in directive '#pragma omp parallel for'
<source>:15:47: error: unexpected OpenMP clause 'induction' in directive '#pragma omp parallel for'
<source>:15:47: error: unexpected OpenMP clause 'induction' in directive '#pragma omp parallel for'
<source>:15:47: error: unexpected OpenMP clause 'induction' in directive '#pragma omp parallel for'
<source>:15:47: error: unexpected OpenMP clause 'induction' in directive '#pragma omp parallel for'
<source>:15:47: error: unexpected OpenMP clause 'induction' in directive '#pragma omp parallel for'
fatal error: too many errors emitted, stopping now [-ferror-limit=]
```
e.g. with the following source code, shortened from the OpenMP examples:
```c
// Taken from https://github.com/OpenMP/Examples/blob/3e4757ae2b52e51df6cd5d363d6fc1d894509719/data_environment/sources/induction.1.c
#include <stdio.h>
void comp_poly(int N, double x, double c[]) {
// x: input: value of x for which to eval the polynomial
// c[N]: input: the coefficients
double x0 = 1.0; // initial value x^0 == 1
double xi; // x^i
double result; // accumulator for the result
// Case 1: induction clause
xi = x0;
result = 0.0;
#pragma omp parallel for reduction(+: result) induction(step(x),*: xi)
for (int i = 0; i < N; i++) {
result += c[i] * xi;
xi *= x;
}
printf("C1: result = %f, xn = %f\n", result, xi);
}
```
built with: `clang -c -fopenmp induction.1.c`.
----
While that is fine in itself, Clang will not terminate and has to be terminated manually.
A backtrace attached to the executing process yields:
```
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
0x000055555c509dc1 in llvm::omp::getOpenMPClauseKindAndVersions(llvm::StringRef) ()
(gdb) bt
#0 0x000055555c509dc1 in llvm::omp::getOpenMPClauseKindAndVersions(llvm::StringRef) ()
#1 0x000055555a9827bd in clang::Parser::ParseOpenMPExecutableDirective(clang::Parser::ParsedStmtContext, llvm::omp::Directive, clang::SourceLocation, bool) ()
#2 0x000055555a98f17d in clang::Parser::ParseOpenMPDeclarativeOrExecutableDirective(clang::Parser::ParsedStmtContext, bool) ()
#3 0x000055555a9b14df in clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector<clang::Stmt*, 24u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::LabelDecl*) ()
#4 0x000055555a9b2b2e in clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 24u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::LabelDecl*) ()
#5 0x000055555a9ba537 in clang::Parser::ParseCompoundStatementBody(bool) ()
#6 0x000055555a9badbf in clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) ()
#7 0x000055555a8b44ef in clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) ()
#8 0x000055555a8f859a in clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo&, clang::SourceLocation*, clang::Parser::ForRangeInit*) ()
#9 0x000055555a8add7c in clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) ()
#10 0x000055555a8ae55f in clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) ()
#11 0x000055555a8b8a61 in clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) ()
#12 0x000055555a8b9a9f in clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) ()
#13 0x000055555a896aca in clang::ParseAST(clang::Sema&, bool, bool) ()
#14 0x000055555902f4c9 in clang::FrontendAction::Execute() ()
#15 0x0000555558fabe25 in clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) ()
#16 0x0000555559129193 in clang::ExecuteCompilerInvocation(clang::CompilerInstance*) ()
#17 0x00005555563e2e30 in cc1_main(llvm::ArrayRef<char const*>, char const*, void*) ()
#18 0x00005555563d939a in ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&, llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>) ()
#19 0x00005555563dd688 in clang_main(int, char**, llvm::ToolContext const&) ()
#20 0x00005555562ea141 in main ()
```
As far as I can tell, this only affects LLVM 22 and trunk. LLVM 21.1.8 simply ignores these directives and yields:
```
warning: extra tokens at the end of '#pragma omp parallel for' are ignored [-Wextra-tokens]
15 | #pragma omp parallel for reduction(+: result) induction(step(x),*: xi)
| ^
1 warning generated.
```
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