Relax unsafe use check. If there is one unconditional use inside the loop then it is safe to promote value even if there is another conditional use inside the loop.

llvm-svn: 42493

2 files changed, 43 insertions, 22 deletions

diff --git a/llvm/lib/Transforms/Scalar/LICM.cpp b/llvm/lib/Transforms/Scalar/LICM.cpp
index e461c887ea2..e795aa9c0c5 100644
--- a/llvm/lib/Transforms/Scalar/LICM.cpp
+++ b/llvm/lib/Transforms/Scalar/LICM.cpp
@@ -800,24 +800,15 @@ void LICM::FindPromotableValuesInLoop(
           break;
         }
 
-      // Do not promote null values because it may be unsafe to do so.
-      if (isa<ConstantPointerNull>(V))
-        PointerOk = false;
-
-      if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) {
-        // If GEP base is NULL then the calculated address used by Store or
-        // Load instruction is invalid. Do not promote this value because
-        // it may expose load and store instruction that are covered by
-        // condition which may not yet folded.
-        if (isa<ConstantPointerNull>(GEP->getOperand(0)))
-          PointerOk = false;
-      }
-
-      // If value V use is not dominating loop exit then promoting
-      // it may expose unsafe load and store instructions unconditinally.
-      if (PointerOk)
+      // If one use of value V inside the loop is safe then it is OK to promote 
+      // this value. On the otherside if there is not any unsafe use inside the
+      // looop then also it is OK to  promote this value. Otherwise it is
+      // unsafe to promote this value.
+      if (PointerOk) {
+        bool oneSafeUse = false;
+        bool oneUnsafeUse = false;
         for(Value::use_iterator UI = V->use_begin(), UE = V->use_end();
-            UI != UE && PointerOk; ++UI) {
+            UI != UE; ++UI) {
           Instruction *Use = dyn_cast<Instruction>(*UI);
           if (!Use || !CurLoop->contains(Use->getParent()))
             continue;
@@ -825,16 +816,25 @@ void LICM::FindPromotableValuesInLoop(
                  ExitI = LoopExits.begin(), ExitE = LoopExits.end();
                ExitI != ExitE; ++ExitI) {
             Instruction *Ex = *ExitI;
-            if (!DT->dominates(Use, Ex)){
-              PointerOk = false;
+            if (!isa<PHINode>(Use) && DT->dominates(Use, Ex)) {
+              oneSafeUse = true;
               break;
             }
+            else 
+              oneUnsafeUse = true;
           }
-          
-          if (!PointerOk)
+
+          if (oneSafeUse)
             break;
         }
-      
+
+        if (oneSafeUse)
+          PointerOk = true;
+        else if (!oneUnsafeUse)
+          PointerOk = true;
+        else
+          PointerOk = false;
+      }
       
       if (PointerOk) {
         const Type *Ty = cast<PointerType>(V->getType())->getElementType();
diff --git a/llvm/test/Transforms/LICM/2007-10-01-PromoteSafeValue.ll b/llvm/test/Transforms/LICM/2007-10-01-PromoteSafeValue.ll
new file mode 100644
index 00000000000..7359cc0695a
--- /dev/null
+++ b/llvm/test/Transforms/LICM/2007-10-01-PromoteSafeValue.ll
@@ -0,0 +1,21 @@
+; RUN: llvm-as < %s | opt -licm | llvm-dis | grep promoted
+; Promote value if at least one use is safe
+
+
+define i32 @f2(i32* %p, i8* %q) {
+entry:
+        br label %loop.head
+
+loop.head:              ; preds = %cond.true, %entry
+        store i32 20, i32* %p
+        %tmp3.i = icmp eq i8* null, %q            ; <i1> [#uses=1]
+        br i1 %tmp3.i, label %exit, label %cond.true
+        
+cond.true:              ; preds = %loop.head
+        store i32 40, i32* %p
+        br label %loop.head
+
+exit:           ; preds = %loop.head
+        ret i32 0
+}
+