Tighten known bits for ctpop based on zero input bits

[oota-llvm.git] / lib / Analysis / Loads.cpp

diff --git a/lib/Analysis/Loads.cpp b/lib/Analysis/Loads.cpp
index 4d6d960f159abcc76a5cc9ad025aeecf1b4707af..4b2fa3c6505a14a1e0b4a5a1eacc9abe5aa7cab6 100644 (file)
--- a/lib/Analysis/Loads.cpp
+++ b/lib/Analysis/Loads.cpp
@@ -118,7 +118,8 @@ bool llvm::isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom,
   // from/to.  If so, the previous load or store would have already trapped,
   // so there is no harm doing an extra load (also, CSE will later eliminate
   // the load entirely).
-  BasicBlock::iterator BBI = ScanFrom, E = ScanFrom->getParent()->begin();
+  BasicBlock::iterator BBI = ScanFrom->getIterator(),
+                       E = ScanFrom->getParent()->begin();
 
   // We can at least always strip pointer casts even though we can't use the
   // base here.
@@ -161,6 +162,18 @@ bool llvm::isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom,
   return false;
 }
 
+/// DefMaxInstsToScan - the default number of maximum instructions
+/// to scan in the block, used by FindAvailableLoadedValue().
+/// FindAvailableLoadedValue() was introduced in r60148, to improve jump
+/// threading in part by eliminating partially redundant loads.
+/// At that point, the value of MaxInstsToScan was already set to '6'
+/// without documented explanation.
+cl::opt<unsigned>
+llvm::DefMaxInstsToScan("available-load-scan-limit", cl::init(6), cl::Hidden,
+  cl::desc("Use this to specify the default maximum number of instructions "
+           "to scan backward from a given instruction, when searching for "
+           "available loaded value"));
+
 /// \brief Scan the ScanBB block backwards to see if we have the value at the
 /// memory address *Ptr locally available within a small number of instructions.
 ///
@@ -199,7 +212,7 @@ Value *llvm::FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB,
   while (ScanFrom != ScanBB->begin()) {
     // We must ignore debug info directives when counting (otherwise they
     // would affect codegen).
-    Instruction *Inst = --ScanFrom;
+    Instruction *Inst = &*--ScanFrom;
     if (isa<DbgInfoIntrinsic>(Inst))
       continue;