ARM / x86_64 varargs: Don't save regparms in prologue without va_start

There's no need to do this if the user doesn't call va_start. In the
future, we're going to have thunks that forward these register
parameters with musttail calls, and they won't need these spills for
handling va_start.

Most of the test suite changes are adding va_start calls to existing
tests to keep things working.

llvm-svn: 216294

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp b/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
index 1c85248eb84..c9da6fd83ee 100644
--- a/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
@@ -138,6 +138,14 @@ void FunctionLoweringInfo::set(const Function &fn, MachineFunction &mf,
         }
       }
 
+      // Look for calls to the @llvm.va_start intrinsic. We can omit some
+      // prologue boilerplate for variadic functions that don't examine their
+      // arguments.
+      if (const auto *II = dyn_cast<IntrinsicInst>(I)) {
+        if (II->getIntrinsicID() == Intrinsic::vastart)
+          MF->getFrameInfo()->setHasVAStart(true);
+      }
+
       // Mark values used outside their block as exported, by allocating
       // a virtual register for them.
       if (isUsedOutsideOfDefiningBlock(I))