[InstCombineCalls] Use isKnownNonNullAt() to check nullness of passing arguments at callsite

Summary: This patch replaces isKnownNonNull() with isKnownNonNullAt() when checking nullness of passing arguments at callsite. In this way it can handle cases where the argument does not have nonnull attribute but has a dominating null check from the CFG. It also adds assertions in isKnownNonNull() and isKnownNonNullFromDominatingCondition() to make sure the value checked is pointer type (as defined in LLVM document). These assertions might trip failures in things which are not  covered under llvm/test, but fixes should be pretty obvious. 

Reviewers: reames

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D12779

llvm-svn: 247587

llvm/lib/Analysis/ValueTracking.cpp

@@ -3220,6 +3220,8 @@ bool llvm::mayBeMemoryDependent(const Instruction &I) {
 
 /// Return true if we know that the specified value is never null.
 bool llvm::isKnownNonNull(const Value *V, const TargetLibraryInfo *TLI) {
+  assert(V->getType()->isPointerTy() && "V must be pointer type");
+
   // Alloca never returns null, malloc might.
   if (isa<AllocaInst>(V)) return true;
 
@@ -3252,6 +3254,8 @@ bool llvm::isKnownNonNull(const Value *V, const TargetLibraryInfo *TLI) {
 static bool isKnownNonNullFromDominatingCondition(const Value *V,
                                                   const Instruction *CtxI,
                                                   const DominatorTree *DT) {
+  assert(V->getType()->isPointerTy() && "V must be pointer type");
+
   unsigned NumUsesExplored = 0;
   for (auto U : V->users()) {
     // Avoid massive lists

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -1583,8 +1583,8 @@ Instruction *InstCombiner::visitCallSite(CallSite CS) {
   // checks on their arguments.
   unsigned ArgNo = 0;
   for (Value *V : CS.args()) {
-    if (!CS.paramHasAttr(ArgNo+1, Attribute::NonNull) &&
-        isKnownNonNull(V)) {
+    if (V->getType()->isPointerTy() && !CS.paramHasAttr(ArgNo+1, Attribute::NonNull) &&
+        isKnownNonNullAt(V, CS.getInstruction(), DT, TLI)) {
       AttributeSet AS = CS.getAttributes();
       AS = AS.addAttribute(CS.getInstruction()->getContext(), ArgNo+1,
                            Attribute::NonNull);

llvm/test/Transforms/InstCombine/call_nonnull_arg.ll

@@ -0,0 +1,20 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+; InstCombine should mark null-checked argument as nonnull at callsite
+declare void @dummy(i32*, i32)
+
+define void @test(i32* %a, i32 %b) {
+; CHECK-LABEL: @test
+; CHECK: call void @dummy(i32* nonnull %a, i32 %b)
+entry:
+  %cond1 = icmp eq i32* %a, null
+  br i1 %cond1, label %dead, label %not_null
+not_null:
+  %cond2 = icmp eq i32 %b, 0
+  br i1 %cond2, label %dead, label %not_zero
+not_zero:
+  call void @dummy(i32* %a, i32 %b)
+  ret void
+dead:
+  unreachable
+}