Annotate return values of allocation functions with dereferenceable_or_null

Summary:
Example
define dso_local noalias i8* @_Z6maixxnv() local_unnamed_addr #0 {
entry:
  %call = tail call noalias dereferenceable_or_null(64) i8* @malloc(i64 64) #6
  ret i8* %call
}


Reviewers: jdoerfert

Reviewed By: jdoerfert

Subscribers: aaron.ballman, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66651

llvm-svn: 370168

1 files changed, 33 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 1802e8c8780..c3be8c4e9a9 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -4178,8 +4178,41 @@ static IntrinsicInst *findInitTrampoline(Value *Callee) {
   return nullptr;
 }
 
+static void annotateAnyAllocSite(CallBase &Call, const TargetLibraryInfo *TLI) {
+  ConstantInt *Op0C = dyn_cast<ConstantInt>(Call.getOperand(0));
+  ConstantInt *Op1C = (Call.getNumArgOperands() == 1)
+                          ? nullptr
+                          : dyn_cast<ConstantInt>(Call.getOperand(1));
+  if ((Op0C && Op0C->isNullValue()) || (Op1C && Op1C->isNullValue()))
+    return;
+  if (isMallocLikeFn(&Call, TLI) && Op0C) {
+    Call.addAttribute(AttributeList::ReturnIndex,
+                      Attribute::getWithDereferenceableOrNullBytes(
+                          Call.getContext(), Op0C->getZExtValue()));
+  } else if (isOpNewLikeFn(&Call, TLI) && Op0C) {
+    Call.addAttribute(AttributeList::ReturnIndex,
+                      Attribute::getWithDereferenceableBytes(
+                          Call.getContext(), Op0C->getZExtValue()));
+  } else if (isReallocLikeFn(&Call, TLI) && Op1C) {
+    Call.addAttribute(AttributeList::ReturnIndex,
+                      Attribute::getWithDereferenceableOrNullBytes(
+                          Call.getContext(), Op1C->getZExtValue()));
+  } else if (isCallocLikeFn(&Call, TLI) && Op0C && Op1C) {
+    bool Overflow;
+    const APInt &N = Op0C->getValue();
+    APInt Size = N.umul_ov(Op1C->getValue(), Overflow);
+    if (!Overflow)
+      Call.addAttribute(AttributeList::ReturnIndex,
+                        Attribute::getWithDereferenceableOrNullBytes(
+                            Call.getContext(), Size.getZExtValue()));
+  }
+}
+
 /// Improvements for call, callbr and invoke instructions.
 Instruction *InstCombiner::visitCallBase(CallBase &Call) {
+  if (isAllocationFn(&Call, &TLI))
+    annotateAnyAllocSite(Call, &TLI);
+
   if (isAllocLikeFn(&Call, &TLI))
     return visitAllocSite(Call);