SwiftTailCC: teach verifier musttail rules applicable to this CC.

SwiftTailCC has a different set of requirements than the C calling convention
for a tail call. The exact argument sequence doesn't have to match, but fewer
ABI-affecting attributes are allowed.

Also make sure the musttail diagnostic triggers if a musttail call isn't
actually a tail call.

1 files changed, 5 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 08ca62b..ab77ef4 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -2924,7 +2924,7 @@ void SelectionDAGBuilder::visitInvoke(const InvokeInst &I) {
     // with deopt state.
     LowerCallSiteWithDeoptBundle(&I, getValue(Callee), EHPadBB);
   } else {
-    LowerCallTo(I, getValue(Callee), false, EHPadBB);
+    LowerCallTo(I, getValue(Callee), false, false, EHPadBB);
   }
 
   // If the value of the invoke is used outside of its defining block, make it
@@ -5734,7 +5734,7 @@ void SelectionDAGBuilder::lowerCallToExternalSymbol(const CallInst &I,
   SDValue Callee = DAG.getExternalSymbol(
       FunctionName,
       DAG.getTargetLoweringInfo().getPointerTy(DAG.getDataLayout()));
-  LowerCallTo(I, Callee, I.isTailCall());
+  LowerCallTo(I, Callee, I.isTailCall(), I.isMustTailCall());
 }
 
 /// Given a @llvm.call.preallocated.setup, return the corresponding
@@ -7420,6 +7420,7 @@ SelectionDAGBuilder::lowerInvokable(TargetLowering::CallLoweringInfo &CLI,
 
 void SelectionDAGBuilder::LowerCallTo(const CallBase &CB, SDValue Callee,
                                       bool isTailCall,
+                                      bool isMustTailCall,
                                       const BasicBlock *EHPadBB) {
   auto &DL = DAG.getDataLayout();
   FunctionType *FTy = CB.getFunctionType();
@@ -7436,7 +7437,7 @@ void SelectionDAGBuilder::LowerCallTo(const CallBase &CB, SDValue Callee,
     // attribute.
     auto *Caller = CB.getParent()->getParent();
     if (Caller->getFnAttribute("disable-tail-calls").getValueAsString() ==
-        "true")
+        "true" && !isMustTailCall)
       isTailCall = false;
 
     // We can't tail call inside a function with a swifterror argument. Lowering
@@ -8060,7 +8061,7 @@ void SelectionDAGBuilder::visitCall(const CallInst &I) {
     // Check if we can potentially perform a tail call. More detailed checking
     // is be done within LowerCallTo, after more information about the call is
     // known.
-    LowerCallTo(I, Callee, I.isTailCall());
+    LowerCallTo(I, Callee, I.isTailCall(), I.isMustTailCall());
 }
 
 namespace {