It's too risky to eliminate sext / zext of call results for tail call optimization even if the caller / callee attributes completely match. The callee may have been bitcast'ed (or otherwise lied about what it's doing).

llvm-svn: 95282

1 files changed, 4 insertions, 6 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 3a25714f07c..201e899bd6a 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -4213,12 +4213,6 @@ isInTailCallPosition(CallSite CS, Attributes CalleeRetAttr,
   // causing miscompilation that has not been fully understood.
   if (!Ret) return false;
 
-  // Unless we are explicitly forcing tailcall optimization do not tailcall if
-  // the called function is bitcast'ed. The analysis may not be entirely
-  // accurate.
-  if (!PerformTailCallOpt && isa<BitCastInst>(CS.getCalledValue()))
-    return false;
-
   // If I will have a chain, make sure no other instruction that will have a
   // chain interposes between I and the return.
   if (I->mayHaveSideEffects() || I->mayReadFromMemory() ||
@@ -4246,6 +4240,10 @@ isInTailCallPosition(CallSite CS, Attributes CalleeRetAttr,
   if ((CalleeRetAttr ^ CallerRetAttr) & ~Attribute::NoAlias)
     return false;
 
+  // It's not safe to eliminate thee sign / zero extension of the return value.
+  if ((CallerRetAttr & Attribute::ZExt) || (CallerRetAttr & Attribute::SExt))
+    return false;
+
   // Otherwise, make sure the unmodified return value of I is the return value.
   for (const Instruction *U = dyn_cast<Instruction>(Ret->getOperand(0)); ;
        U = dyn_cast<Instruction>(U->getOperand(0))) {