Move tail call disabling code to target independent code

When the "disable-tail-calls" attribute was added, checks were added for
it in various backends. Now this code has proliferated, and it is
something the target is responsible for checking. Move that
responsibility back to the ISels (fast, global, and SD).

There's no major functionality change, except for targets that never
implemented this check.

This LLVM attribute was originally added in
d9699bc7bdf0362173fcd256690f61a4d47429c2 (2015).

Reviewers: echristo, MaskRay

Differential Revision: https://reviews.llvm.org/D72118

1 files changed, 4 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 1049a897c6f..9d33c53dd4f 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -52,6 +52,10 @@ bool TargetLowering::isInTailCallPosition(SelectionDAG &DAG, SDNode *Node,
                                           SDValue &Chain) const {
   const Function &F = DAG.getMachineFunction().getFunction();
 
+  // First, check if tail calls have been disabled in this function.
+  if (F.getFnAttribute("disable-tail-calls").getValueAsString() == "true")
+    return false;
+
   // Conservatively require the attributes of the call to match those of
   // the return. Ignore NoAlias and NonNull because they don't affect the
   // call sequence.