Add a little heuristic to Value::isUsedInBasicBlock to speed it up for small basic blocks.
- Calling getUser in a loop is much more expensive than iterating over a few instructions.
- Use it instead of the open-coded loop in AddrModeMatcher.
- 5% speedup on ARMDisassembler.cpp Release builds.
llvm-svn: 145810
diff --git a/llvm/lib/VMCore/Value.cpp b/llvm/lib/VMCore/Value.cpp
index 291df91..a5f1918 100644
--- a/llvm/lib/VMCore/Value.cpp
+++ b/llvm/lib/VMCore/Value.cpp
@@ -108,6 +108,19 @@
/// isUsedInBasicBlock - Return true if this value is used in the specified
/// basic block.
bool Value::isUsedInBasicBlock(const BasicBlock *BB) const {
+ // Start by scanning over the instructions looking for a use before we start
+ // the expensive use iteration.
+ unsigned MaxBlockSize = 3;
+ for (BasicBlock::const_iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
+ if (std::find(I->op_begin(), I->op_end(), this) != I->op_end())
+ return true;
+ if (MaxBlockSize-- == 0) // If the block is larger fall back to use_iterator
+ break;
+ }
+
+ if (MaxBlockSize != 0) // We scanned the entire block and found no use.
+ return false;
+
for (const_use_iterator I = use_begin(), E = use_end(); I != E; ++I) {
const Instruction *User = dyn_cast<Instruction>(*I);
if (User && User->getParent() == BB)