A dead malloc, a free(NULL) and a free(undef) are all trivially dead

instructions.

This doesn't introduce any optimizations we weren't doing before (except
potentially due to pass ordering issues), now passes will eliminate them sooner
as part of their own cleanups.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142787 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Utils/Local.cpp

@@ -28,6 +28,7 @@
 #include "llvm/Analysis/DIBuilder.h"
 #include "llvm/Analysis/Dominators.h"
 #include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Analysis/MemoryBuiltins.h"
 #include "llvm/Analysis/ProfileInfo.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/Target/TargetData.h"
@@ -257,6 +258,13 @@ bool llvm::isInstructionTriviallyDead(Instruction *I) {
         II->getIntrinsicID() == Intrinsic::lifetime_end)
       return isa<UndefValue>(II->getArgOperand(1));
   }
+
+  if (extractMallocCall(I)) return true;
+
+  if (CallInst *CI = isFreeCall(I))
+    if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
+      return C->isNullValue() || isa<UndefValue>(C);
+
   return false;
 }
 

test/Transforms/DeadStoreElimination/simple.ll

@@ -257,5 +257,4 @@ define void @test20() {
   ret void
 }
 ; CHECK: @test20
-; CHECK-NOT: store
-; CHECK: ret void
+; CHECK-NEXT: ret void