[CodeGen] Enable tail calls for functions with NonNull attributes.

Adding NonNull as attributes to returned pointers has the unfortunate side
effect of disabling tail calls. This patch ignores the NonNull attribute when
we decide whether to tail merge, in the same way that we ignore the NoAlias
attribute, as it has no affect on the call sequence.

Differential Revision: https://reviews.llvm.org/D52238

llvm-svn: 343091

3 files changed, 7 insertions, 12 deletions

diff --git a/llvm/lib/CodeGen/Analysis.cpp b/llvm/lib/CodeGen/Analysis.cpp
index 7c1fb6879a6..b769e92590f 100644
--- a/llvm/lib/CodeGen/Analysis.cpp
+++ b/llvm/lib/CodeGen/Analysis.cpp
@@ -519,10 +519,12 @@ bool llvm::attributesPermitTailCall(const Function *F, const Instruction *I,
   AttrBuilder CalleeAttrs(cast<CallInst>(I)->getAttributes(),
                           AttributeList::ReturnIndex);
 
-  // Noalias is completely benign as far as calling convention goes, it
-  // shouldn't affect whether the call is a tail call.
+  // NoAlias and NonNull are completely benign as far as calling convention
+  // goes, they shouldn't affect whether the call is a tail call.
   CallerAttrs.removeAttribute(Attribute::NoAlias);
   CalleeAttrs.removeAttribute(Attribute::NoAlias);
+  CallerAttrs.removeAttribute(Attribute::NonNull);
+  CalleeAttrs.removeAttribute(Attribute::NonNull);
 
   if (CallerAttrs.contains(Attribute::ZExt)) {
     if (!CalleeAttrs.contains(Attribute::ZExt))
diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index ec4451ffa75..d69e9589976 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -1871,15 +1871,6 @@ bool CodeGenPrepare::dupRetToEnableTailCallOpts(BasicBlock *BB) {
     CallInst *CI = TailCalls[i];
     CallSite CS(CI);
 
-    // Conservatively require the attributes of the call to match those of the
-    // return. Ignore noalias because it doesn't affect the call sequence.
-    AttributeList CalleeAttrs = CS.getAttributes();
-    if (AttrBuilder(CalleeAttrs, AttributeList::ReturnIndex)
-            .removeAttribute(Attribute::NoAlias) !=
-        AttrBuilder(CalleeAttrs, AttributeList::ReturnIndex)
-            .removeAttribute(Attribute::NoAlias))
-      continue;
-
     // Make sure the call instruction is followed by an unconditional branch to
     // the return block.
     BasicBlock *CallBB = CI->getParent();
diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index d7d4bef8d3c..46c2f8ebfb8 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -55,10 +55,12 @@ bool TargetLowering::isInTailCallPosition(SelectionDAG &DAG, SDNode *Node,
   const Function &F = DAG.getMachineFunction().getFunction();
 
   // Conservatively require the attributes of the call to match those of
-  // the return. Ignore noalias because it doesn't affect the call sequence.
+  // the return. Ignore NoAlias and NonNull because they don't affect the
+  // call sequence.
   AttributeList CallerAttrs = F.getAttributes();
   if (AttrBuilder(CallerAttrs, AttributeList::ReturnIndex)
           .removeAttribute(Attribute::NoAlias)
+          .removeAttribute(Attribute::NonNull)
           .hasAttributes())
     return false;