[llvm-commits] [llvm] r118875 - in /llvm/trunk: lib/Transforms/Scalar/DeadStoreElimination.cpp test/Transforms/DeadStoreElimination/free.ll

[Dan Gohman]

Author: djg
Date: Thu Nov 11 20:19:17 2010
New Revision: 118875

URL: http://llvm.org/viewvc/llvm-project?rev=118875&view=rev
Log:
Enhance DSE to handle the case where a free call makes more than
one store dead. This is especially noticeable in
SingleSource/Benchmarks/Shootout/objinst.

Modified:
    llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp
    llvm/trunk/test/Transforms/DeadStoreElimination/free.ll

Modified: llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp?rev=118875&r1=118874&r2=118875&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp Thu Nov 11 20:19:17 2010
@@ -59,6 +59,7 @@
     
     bool runOnBasicBlock(BasicBlock &BB);
     bool handleFreeWithNonTrivialDependency(const CallInst *F,
+                                            Instruction *Inst,
                                             MemDepResult Dep);
     bool handleEndBlock(BasicBlock &BB);
     bool RemoveUndeadPointers(Value *Ptr, uint64_t killPointerSize,
@@ -212,7 +213,7 @@
   
     // Handle frees whose dependencies are non-trivial.
     if (const CallInst *F = isFreeCall(Inst)) {
-      MadeChange |= handleFreeWithNonTrivialDependency(F, InstDep);
+      MadeChange |= handleFreeWithNonTrivialDependency(F, Inst, InstDep);
       continue;
     }
     
@@ -298,23 +299,34 @@
 /// handleFreeWithNonTrivialDependency - Handle frees of entire structures whose
 /// dependency is a store to a field of that structure.
 bool DSE::handleFreeWithNonTrivialDependency(const CallInst *F,
+                                             Instruction *Inst,
                                              MemDepResult Dep) {
   AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
+  MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();
   
-  Instruction *Dependency = Dep.getInst();
-  if (!Dependency || !doesClobberMemory(Dependency) || !isElidable(Dependency))
-    return false;
+  do {
+    Instruction *Dependency = Dep.getInst();
+    if (!Dependency || !doesClobberMemory(Dependency) || !isElidable(Dependency))
+      return false;
   
-  Value *DepPointer = getPointerOperand(Dependency)->getUnderlyingObject();
+    Value *DepPointer = getPointerOperand(Dependency)->getUnderlyingObject();
 
-  // Check for aliasing.
-  if (AA.alias(F->getArgOperand(0), 1, DepPointer, 1) !=
-         AliasAnalysis::MustAlias)
-    return false;
+    // Check for aliasing.
+    if (AA.alias(F->getArgOperand(0), 1, DepPointer, 1) !=
+           AliasAnalysis::MustAlias)
+      return false;
   
-  // DCE instructions only used to calculate that store
-  DeleteDeadInstruction(Dependency);
-  ++NumFastStores;
+    // DCE instructions only used to calculate that store
+    DeleteDeadInstruction(Dependency);
+    ++NumFastStores;
+
+    // Inst's old Dependency is now deleted. Compute the next dependency,
+    // which may also be dead, as in
+    //    s[0] = 0;
+    //    s[1] = 0; // This has just been deleted.
+    //    free(s);
+    Dep = MD.getDependency(Inst);
+  } while (!Dep.isNonLocal());
   return true;
 }
 

Modified: llvm/trunk/test/Transforms/DeadStoreElimination/free.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/DeadStoreElimination/free.ll?rev=118875&r1=118874&r2=118875&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/DeadStoreElimination/free.ll (original)
+++ llvm/trunk/test/Transforms/DeadStoreElimination/free.ll Thu Nov 11 20:19:17 2010
@@ -24,3 +24,17 @@
 	ret void
 }
 
+; CHECK: @test4
+; CHECK-NOT: store
+; CHECK: ret void
+define void @test4() {
+  %m = call i8* @malloc(i64 24)
+  store i8 0, i8* %m
+  %m1 = getelementptr i8* %m, i64 1
+  store i8 1, i8* %m1
+  call void @free(i8* %m)
+  ret void
+}
+
+declare void @free(i8*)
+declare i8* @malloc(i64)