Recognize while(1) and avoid extra blocks.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@42811 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/CodeGen/CGStmt.cpp b/CodeGen/CGStmt.cpp
index 226462b..3a55e04 100644
--- a/CodeGen/CGStmt.cpp
+++ b/CodeGen/CGStmt.cpp
@@ -169,9 +169,13 @@
// of the controlling expression takes place before each execution of the loop
// body.
llvm::Value *BoolCondVal = EvaluateExprAsBool(S.getCond());
-
- // TODO: while(1) is common, avoid extra exit blocks, etc. Be sure
+
+ // while(1) is common, avoid extra exit blocks. Be sure
// to correctly handle break/continue though.
+ bool EmitBoolCondBranch = true;
+ if (llvm::ConstantInt *C = dyn_cast<llvm::ConstantInt>(BoolCondVal))
+ if (C->isOne())
+ EmitBoolCondBranch = false;
// Create an exit block for when the condition fails, create a block for the
// body of the loop.
@@ -179,7 +183,8 @@
llvm::BasicBlock *LoopBody = new llvm::BasicBlock("whilebody");
// As long as the condition is true, go to the loop body.
- Builder.CreateCondBr(BoolCondVal, LoopBody, ExitBlock);
+ if (EmitBoolCondBranch)
+ Builder.CreateCondBr(BoolCondVal, LoopBody, ExitBlock);
// Store the blocks to use for break and continue.
BreakContinueStack.push_back(BreakContinue(ExitBlock, LoopHeader));
@@ -195,6 +200,14 @@
// Emit the exit block.
EmitBlock(ExitBlock);
+
+ // If LoopHeader is a simple forwarding block then eliminate it.
+ if (!EmitBoolCondBranch
+ && &LoopHeader->front() == LoopHeader->getTerminator()) {
+ LoopHeader->replaceAllUsesWith(LoopBody);
+ LoopHeader->getTerminator()->eraseFromParent();
+ LoopHeader->eraseFromParent();
+ }
}
void CodeGenFunction::EmitDoStmt(const DoStmt &S) {
@@ -231,7 +244,6 @@
if (C->isZero())
EmitBoolCondBranch = false;
-
// As long as the condition is true, iterate the loop.
if (EmitBoolCondBranch)
Builder.CreateCondBr(BoolCondVal, LoopBody, AfterDo);