[AArch64][GlobalISel] Support lowering variadic musttail calls

This adds support for lowering variadic musttail calls. To do this, we have
to...

- Detect a musttail call in a variadic function before attempting to lower the
  call's formal arguments. This is done in the IRTranslator.
- Compute forwarded registers in `lowerFormalArguments`, and add copies for
  those registers.
- Restore the forwarded registers in `lowerTailCall`.

Because there doesn't seem to be any nice way to wrap these up into the outgoing
argument handler, the restore code in `lowerTailCall` is done separately.

Also, irritatingly, you have to make sure that the registers don't overlap with
any passed parameters. Otherwise, the scheduler doesn't know what to do with the
extra copies and asserts.

Add call-translator-variadic-musttail.ll to test this. This is pretty much the
same as the X86 musttail-varargs.ll test. We didn't have as nice of a test to
base this off of, but the idea is the same.

Differential Revision: https://reviews.llvm.org/D68043

llvm-svn: 373226

1 files changed, 22 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
index 58c444d129d..37ac96e5290 100644
--- a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
@@ -2193,6 +2193,20 @@ void IRTranslator::finalizeFunction() {
   FuncInfo.clear();
 }
 
+/// Returns true if a BasicBlock \p BB within a variadic function contains a
+/// variadic musttail call.
+static bool checkForMustTailInVarArgFn(bool IsVarArg, const BasicBlock &BB) {
+  if (!IsVarArg)
+    return false;
+
+  // Walk the block backwards, because tail calls usually only appear at the end
+  // of a block.
+  return std::any_of(BB.rbegin(), BB.rend(), [](const Instruction &I) {
+    const auto *CI = dyn_cast<CallInst>(&I);
+    return CI && CI->isMustTailCall();
+  });
+}
+
 bool IRTranslator::runOnMachineFunction(MachineFunction &CurMF) {
   MF = &CurMF;
   const Function &F = MF->getFunction();
@@ -2254,6 +2268,9 @@ bool IRTranslator::runOnMachineFunction(MachineFunction &CurMF) {
   SwiftError.setFunction(CurMF);
   SwiftError.createEntriesInEntryBlock(DbgLoc);
 
+  bool IsVarArg = F.isVarArg();
+  bool HasMustTailInVarArgFn = false;
+
   // Create all blocks, in IR order, to preserve the layout.
   for (const BasicBlock &BB: F) {
     auto *&MBB = BBToMBB[&BB];
@@ -2263,8 +2280,13 @@ bool IRTranslator::runOnMachineFunction(MachineFunction &CurMF) {
 
     if (BB.hasAddressTaken())
       MBB->setHasAddressTaken();
+
+    if (!HasMustTailInVarArgFn)
+      HasMustTailInVarArgFn = checkForMustTailInVarArgFn(IsVarArg, BB);
   }
 
+  MF->getFrameInfo().setHasMustTailInVarArgFunc(HasMustTailInVarArgFn);
+
   // Make our arguments/constants entry block fallthrough to the IR entry block.
   EntryBB->addSuccessor(&getMBB(F.front()));