[Verifier] Reject va_start in non-variadic function (llvm#88809)

A va_start intrinsic lowers to something derived from the variadic
parameter to the function. If there is no such parameter, it can't lower
meaningfully. Clang sema rejects the same with `error: 'va_start' used
in function with fixed args`.

Moves the existing lint warning into a verifier error. Updates the one
lit test that had a va_start in a non-variadic function.

llvm/lib/Analysis/Lint.cpp

@@ -350,10 +350,7 @@ void Lint::visitCallBase(CallBase &I) {
     }
 
     case Intrinsic::vastart:
-      Check(I.getParent()->getParent()->isVarArg(),
-            "Undefined behavior: va_start called in a non-varargs function",
-            &I);
-
+      // vastart in non-varargs function is rejected by the verifier
       visitMemoryReference(I, MemoryLocation::getForArgument(&I, 0, TLI),
                            std::nullopt, nullptr, MemRef::Read | MemRef::Write);
       break;

llvm/lib/IR/Verifier.cpp

@@ -5798,6 +5798,11 @@ void Verifier::visitIntrinsicCall(Intrinsic::ID ID, CallBase &Call) {
 
     break;
   }
+  case Intrinsic::vastart: {
+    Check(Call.getFunction()->isVarArg(),
+          "va_start called in a non-varargs function");
+    break;
+  }
   case Intrinsic::vector_reduce_and:
   case Intrinsic::vector_reduce_or:
   case Intrinsic::vector_reduce_xor:

llvm/test/CodeGen/AArch64/GlobalISel/vastart.ll

@@ -3,7 +3,7 @@
 
 
 declare void @llvm.va_start(ptr)
-define void @test_va_start(ptr %list) {
+define void @test_va_start(ptr %list, ...) {
 ; CHECK-LABEL: name: test_va_start
 ; CHECK: [[LIST:%[0-9]+]]:_(p0) = COPY $x0
 ; CHECK-IOS: G_VASTART [[LIST]](p0) :: (store (s64) into %ir.list, align 1)

llvm/test/Other/lint.ll

@@ -124,13 +124,6 @@ define void @0() nounwind {
   ret void
 }
 
-; CHECK: va_start called in a non-varargs function
-declare void @llvm.va_start(ptr)
-define void @not_vararg(ptr %p) nounwind {
-  call void @llvm.va_start(ptr %p)
-  ret void
-}
-
 ; CHECK: Undefined behavior: Branch to non-blockaddress
 define void @use_indbr() {
   indirectbr ptr @foo, [label %block]

llvm/test/Verifier/variadic.ll

@@ -0,0 +1,8 @@
+; RUN: not opt -S -passes=verify 2>&1 < %s | FileCheck %s
+
+; CHECK: va_start called in a non-varargs function
+declare void @llvm.va_start(ptr)
+define void @not_vararg(ptr %p) nounwind {
+  call void @llvm.va_start(ptr %p)
+  ret void
+}