Generalize instcombine's isSafeToLoadUnconditionally() function

to ignore readonly calls, and factor it out of instcombine so
that it can be used by other passes.  Patch by Frits van Bommel!



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73506 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Transforms/Utils/Local.h

@@ -30,6 +30,16 @@ struct DbgInfoIntrinsic;
 
 template<typename T> class SmallVectorImpl;
   
+//===----------------------------------------------------------------------===//
+//  Local analysis.
+//
+
+/// isSafeToLoadUnconditionally - Return true if we know that executing a load
+/// from this value cannot trap.  If it is not obviously safe to load from the
+/// specified pointer, we do a quick local scan of the basic block containing
+/// ScanFrom, to determine if the address is already accessed.
+bool isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom);
+
 //===----------------------------------------------------------------------===//
 //  Local constant propagation.
 //

lib/Transforms/Scalar/InstructionCombining.cpp

@@ -11419,45 +11419,6 @@ static Instruction *InstCombineLoadCast(InstCombiner &IC, LoadInst &LI,
   return 0;
 }
 
-/// isSafeToLoadUnconditionally - Return true if we know that executing a load
-/// from this value cannot trap.  If it is not obviously safe to load from the
-/// specified pointer, we do a quick local scan of the basic block containing
-/// ScanFrom, to determine if the address is already accessed.
-static bool isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom) {
-  // If it is an alloca it is always safe to load from.
-  if (isa<AllocaInst>(V)) return true;
-
-  // If it is a global variable it is mostly safe to load from.
-  if (const GlobalValue *GV = dyn_cast<GlobalVariable>(V))
-    // Don't try to evaluate aliases.  External weak GV can be null.
-    return !isa<GlobalAlias>(GV) && !GV->hasExternalWeakLinkage();
-
-  // Otherwise, be a little bit agressive by scanning the local block where we
-  // want to check to see if the pointer is already being loaded or stored
-  // 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();
-
-  while (BBI != E) {
-    --BBI;
-
-    // If we see a free or a call (which might do a free) the pointer could be
-    // marked invalid.
-    if (isa<FreeInst>(BBI) || 
-        (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)))
-      return false;
-    
-    if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
-      if (LI->getOperand(0) == V) return true;
-    } else if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
-      if (SI->getOperand(1) == V) return true;
-    }
-
-  }
-  return false;
-}
-
 Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
   Value *Op = LI.getOperand(0);
 

lib/Transforms/Utils/Local.cpp

@@ -14,6 +14,7 @@
 
 #include "llvm/Transforms/Utils/Local.h"
 #include "llvm/Constants.h"
+#include "llvm/GlobalAlias.h"
 #include "llvm/GlobalVariable.h"
 #include "llvm/DerivedTypes.h"
 #include "llvm/Instructions.h"
@@ -27,6 +28,50 @@
 #include "llvm/Support/MathExtras.h"
 using namespace llvm;
 
+//===----------------------------------------------------------------------===//
+//  Local analysis.
+//
+
+/// isSafeToLoadUnconditionally - Return true if we know that executing a load
+/// from this value cannot trap.  If it is not obviously safe to load from the
+/// specified pointer, we do a quick local scan of the basic block containing
+/// ScanFrom, to determine if the address is already accessed.
+bool llvm::isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom) {
+  // If it is an alloca it is always safe to load from.
+  if (isa<AllocaInst>(V)) return true;
+
+  // If it is a global variable it is mostly safe to load from.
+  if (const GlobalValue *GV = dyn_cast<GlobalVariable>(V))
+    // Don't try to evaluate aliases.  External weak GV can be null.
+    return !isa<GlobalAlias>(GV) && !GV->hasExternalWeakLinkage();
+
+  // Otherwise, be a little bit agressive by scanning the local block where we
+  // want to check to see if the pointer is already being loaded or stored
+  // 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();
+
+  while (BBI != E) {
+    --BBI;
+
+    // If we see a free or a call which may write to memory (i.e. which might do
+    // a free) the pointer could be marked invalid.
+    if (isa<FreeInst>(BBI) || 
+        (isa<CallInst>(BBI) && BBI->mayWriteToMemory() &&
+         !isa<DbgInfoIntrinsic>(BBI)))
+      return false;
+
+    if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
+      if (LI->getOperand(0) == V) return true;
+    } else if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
+      if (SI->getOperand(1) == V) return true;
+    }
+  }
+  return false;
+}
+
+
 //===----------------------------------------------------------------------===//
 //  Local constant propagation.
 //