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Fix for PR2969: generate a memcpy from a constant for constant

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initializers.  llvm-gcc appears to be more aggressive, but incorrect, 
for constructs like "const int a[] = {1,2,3};"; that said, current 
optimizers will do the appropriate optimizations when safe.

llvm-svn: 60270
This commit is contained in:
Eli Friedman
2008-11-30 02:11:09 +00:00
parent 79ceb0947b
commit c59bb48e80
1 changed files with 17 additions and 8 deletions
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21
clang/lib/CodeGen/CGExprAgg.cpp
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@@ -369,12 +369,21 @@ void AggExprEmitter::VisitInitListExpr(InitListExpr *E) {
return; return;
} }
// FIXME: For constant expressions, call into const expr emitter so // If we can, prefer a copy from a global; this is a lot less
// that we can emit a memcpy instead of storing the individual // code for long globals, and it's easier for the current optimizers
// members. This is purely for perf; both codepaths lead to // to analyze.
// equivalent (although not necessarily identical) code. It's worth // FIXME: Should we really be doing this? Should we try to avoid
// noting that LLVM keeps on getting smarter, though, so it might // cases where we emit a global with a lot of zeros? Should
// not be worth bothering. // we try to avoid short globals?
if (E->isConstantExpr(CGF.getContext(), 0)) {
llvm::Constant* C = CGF.CGM.EmitConstantExpr(E, &CGF);
llvm::GlobalVariable* GV =
new llvm::GlobalVariable(C->getType(), true,
llvm::GlobalValue::InternalLinkage,
C, "", &CGF.CGM.getModule(), 0);
CGF.EmitAggregateCopy(DestPtr, GV, E->getType());
return;
}
// Handle initialization of an array. // Handle initialization of an array.
if (E->getType()->isArrayType()) { if (E->getType()->isArrayType()) {