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Recognize "do {} while (0)" idiom and avoid extra basic blocks. 

llvm-svn: 42808
This commit is contained in:
Devang Patel 2007-10-09 20:33:39 +00:00
parent 7ad0c2f1f9
commit c1380400d5
1 changed files with 18 additions and 5 deletions
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23
clang/CodeGen/CGStmt.cpp
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@ -198,9 +198,6 @@ void CodeGenFunction::EmitWhileStmt(const WhileStmt &S) {
}
void CodeGenFunction::EmitDoStmt(const DoStmt &S) {
// TODO: "do {} while (0)" is common in macros, avoid extra blocks. Be sure
// to correctly handle break/continue though.
// Emit the body for the loop, insert it, which will create an uncond br to
// it.
llvm::BasicBlock *LoopBody = new llvm::BasicBlock("dobody");
@ -226,12 +223,28 @@ void CodeGenFunction::EmitDoStmt(const DoStmt &S) {
// C99 6.8.5p2/p4: The first substatement is executed if the expression
// compares unequal to 0. The condition must be a scalar type.
llvm::Value *BoolCondVal = EvaluateExprAsBool(S.getCond());
// "do {} while (0)" is common in macros, avoid extra blocks. Be sure
// to correctly handle break/continue though.
bool EmitBoolCondBranch = true;
if (llvm::ConstantInt *C = dyn_cast<llvm::ConstantInt>(BoolCondVal))
if (C->isZero())
EmitBoolCondBranch = false;
// As long as the condition is true, iterate the loop.
Builder.CreateCondBr(BoolCondVal, LoopBody, AfterDo);
if (EmitBoolCondBranch)
Builder.CreateCondBr(BoolCondVal, LoopBody, AfterDo);
// Emit the exit block.
EmitBlock(AfterDo);
// If DoCond is a simple forwarding block then eliminate it.
if (!EmitBoolCondBranch && &DoCond->front() == DoCond->getTerminator()) {
DoCond->replaceAllUsesWith(AfterDo);
DoCond->getTerminator()->eraseFromParent();
DoCond->eraseFromParent();
}
}
void CodeGenFunction::EmitForStmt(const ForStmt &S) {