move FindAvailableLoadedValue from JumpThreading to Transforms/Utils.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60166 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp
index eb4a873..ec35a89 100644
--- a/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/lib/Transforms/Scalar/JumpThreading.cpp
@@ -243,67 +243,6 @@
return false;
}
-
-/// FindAvailableLoadedValue - Scan backwards from ScanFrom checking to see if
-/// we have the value at the memory address *Ptr locally available within a
-/// small number of instructions. If the value is available, return it.
-///
-/// If not, return the iterator for the last validated instruction that the
-/// value would be live through. If we scanned the entire block, ScanFrom would
-/// be left at begin().
-///
-/// FIXME: Move this to transform utils and use from
-/// InstCombiner::visitLoadInst. It would also be nice to optionally take AA so
-/// that GVN could do this.
-static Value *FindAvailableLoadedValue(Value *Ptr,
- BasicBlock *ScanBB,
- BasicBlock::iterator &ScanFrom) {
-
- unsigned NumToScan = 6;
- while (ScanFrom != ScanBB->begin()) {
- // Don't scan huge blocks.
- if (--NumToScan == 0) return 0;
-
- Instruction *Inst = --ScanFrom;
-
- // If this is a load of Ptr, the loaded value is available.
- if (LoadInst *LI = dyn_cast<LoadInst>(Inst))
- if (LI->getOperand(0) == Ptr)
- return LI;
-
- if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
- // If this is a store through Ptr, the value is available!
- if (SI->getOperand(1) == Ptr)
- return SI->getOperand(0);
-
- // If Ptr is an alloca and this is a store to a different alloca, ignore
- // the store. This is a trivial form of alias analysis that is important
- // for reg2mem'd code.
- if ((isa<AllocaInst>(Ptr) || isa<GlobalVariable>(Ptr)) &&
- (isa<AllocaInst>(SI->getOperand(1)) ||
- isa<GlobalVariable>(SI->getOperand(1))))
- continue;
-
- // Otherwise the store that may or may not alias the pointer, bail out.
- ++ScanFrom;
- return 0;
- }
-
-
- // If this is some other instruction that may clobber Ptr, bail out.
- if (Inst->mayWriteToMemory()) {
- // May modify the pointer, bail out.
- ++ScanFrom;
- return 0;
- }
- }
-
- // Got to the start of the block, we didn't find it, but are done for this
- // block.
- return 0;
-}
-
-
/// SimplifyPartiallyRedundantLoad - If LI is an obviously partially redundant
/// load instruction, eliminate it by replacing it with a PHI node. This is an
/// important optimization that encourages jump threading, and needs to be run
@@ -330,7 +269,8 @@
// the entry to its block.
BasicBlock::iterator BBIt = LI;
- if (Value *AvailableVal = FindAvailableLoadedValue(LoadedPtr, LoadBB, BBIt)) {
+ if (Value *AvailableVal = FindAvailableLoadedValue(LoadedPtr, LoadBB,
+ BBIt, 6)) {
// If the value if the load is locally available within the block, just use
// it. This frequently occurs for reg2mem'd allocas.
//cerr << "LOAD ELIMINATED:\n" << *BBIt << *LI << "\n";
@@ -363,7 +303,7 @@
// Scan the predecessor to see if the value is available in the pred.
BBIt = PredBB->end();
- Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt);
+ Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt, 6);
if (!PredAvailable) {
OneUnavailablePred = PredBB;
continue;