[llvm-commits] [llvm] r42493 - in /llvm/trunk: lib/Transforms/Scalar/LICM.cpp test/Transforms/LICM/2007-10-01-PromoteSafeValue.ll

[Devang Patel]

Author: dpatel
Date: Mon Oct  1 13:12:58 2007
New Revision: 42493

URL: http://llvm.org/viewvc/llvm-project?rev=42493&view=rev
Log:
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.

Added:
    llvm/trunk/test/Transforms/LICM/2007-10-01-PromoteSafeValue.ll
Modified:
    llvm/trunk/lib/Transforms/Scalar/LICM.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/LICM.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LICM.cpp?rev=42493&r1=42492&r2=42493&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LICM.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LICM.cpp Mon Oct  1 13:12:58 2007
@@ -800,24 +800,15 @@
           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 @@
                  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();

Added: llvm/trunk/test/Transforms/LICM/2007-10-01-PromoteSafeValue.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LICM/2007-10-01-PromoteSafeValue.ll?rev=42493&view=auto

==============================================================================
--- llvm/trunk/test/Transforms/LICM/2007-10-01-PromoteSafeValue.ll (added)
+++ llvm/trunk/test/Transforms/LICM/2007-10-01-PromoteSafeValue.ll Mon Oct  1 13:12:58 2007
@@ -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
+}
+