[LLVMdev] [BUG] Varargs example in LangRef segfaults

[Ramkumar Ramachandra]

Hi,

So the Variable Argument Handling Intrinsics section of the LangRef
(http://llvm.org/docs/LangRef.html#variable-argument-handling-intrinsics)
lists an example that segfaults. Try the following on x86_64:

-- 8< --
define i32 @test(i32 %X, ...) {
  ; Initialize variable argument processing
  %ap = alloca i8*
  %ap2 = bitcast i8** %ap to i8*
  call void @llvm.va_start(i8* %ap2)

  ; Read a single integer argument
  %tmp = va_arg i8** %ap, i32

  ; Demonstrate usage of llvm.va_copy and llvm.va_end
  %aq = alloca i8*
  %aq2 = bitcast i8** %aq to i8*
  call void @llvm.va_copy(i8* %aq2, i8* %ap2)
  call void @llvm.va_end(i8* %aq2)

  ; Stop processing of arguments.
  call void @llvm.va_end(i8* %ap2)
  ret i32 %tmp
}

define i32 @main() {
  %call = call i32 (i32, ...)* @test(i32 1, i32 3)
  ret i32 %call
}

declare void @llvm.va_start(i8*)
declare void @llvm.va_copy(i8*, i8*)
declare void @llvm.va_end(i8*)
-- 8< --

It happens because va_arg is apparently not implemented properly on
X86 (I saw tests/Codegen/X86/vaargs.ll). What should be done about the
situation?
1. Update the LangRef.
2. Fix va_arg for x86.

If (2) is the way to go, I'll take a stab at it.

Thanks.

Ram