我一直在尝试使用LLVM中的模块传递创建一个函数。我要做的是创建一个变量参数函数,然后添加逻辑来操作变量参数。 例如:
/\*can do this\*/
int foo(int a, ...)
{
double var1;
//can't figure out how to add any of this using llvm
va_list ap;
va_start(ap, a);
va_arg(var1,double);
va_end(ap);
}
创建函数类型很简单,因为我只是将vararg boolean设置为true。之后我该怎么办?
答案 0 :(得分:2)
我总是使用clang来检查转换为c / c ++ lang需要什么。 使用llvm指令va_arg和intinsics llvm.va_start,llvm.va_end,llvm.va_copy来使用llvm变量参数支持。
对于对使用此参数的参数进行操作的函数,您还需要特定于目标的值类型“va_list”。
; This struct is different for every platform. For most platforms,
; it is merely an i8*.
%struct.va_list = type { i8* }
; For Unix x86_64 platforms, va_list is the following struct:
; %struct.va_list = type { i32, i32, i8*, i8* }
ref http://llvm.org/docs/LangRef.html#variable-argument-handling-intrinsics
列出的代码,
; ModuleID = 'test.c'
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-pc-linux-gnu"
%struct.__va_list_tag = type { i32, i32, i8*, i8* }
; Function Attrs: nounwind uwtable
define i32 @foo(i32 %a, ...) #0 {
%1 = alloca i32, align 4
%2 = alloca i32, align 4
%var1 = alloca double, align 8
%ap = alloca [1 x %struct.__va_list_tag], align 16
store i32 %a, i32* %2, align 4
%3 = getelementptr inbounds [1 x %struct.__va_list_tag]* %ap, i32 0, i32 0
%4 = bitcast %struct.__va_list_tag* %3 to i8*
call void @llvm.va_start(i8* %4)
%5 = getelementptr inbounds [1 x %struct.__va_list_tag]* %ap, i32 0, i32 0
%6 = getelementptr inbounds %struct.__va_list_tag* %5, i32 0, i32 1
%7 = load i32* %6
%8 = icmp ule i32 %7, 160
br i1 %8, label %9, label %15
; <label>:9 ; preds = %0
%10 = getelementptr inbounds %struct.__va_list_tag* %5, i32 0, i32 3
%11 = load i8** %10
%12 = getelementptr i8* %11, i32 %7
%13 = bitcast i8* %12 to double*
%14 = add i32 %7, 16
store i32 %14, i32* %6
br label %20
; <label>:15 ; preds = %0
%16 = getelementptr inbounds %struct.__va_list_tag* %5, i32 0, i32 2
%17 = load i8** %16
%18 = bitcast i8* %17 to double*
%19 = getelementptr i8* %17, i32 8
store i8* %19, i8** %16
br label %20
; <label>:20 ; preds = %15, %9
%21 = phi double* [ %13, %9 ], [ %18, %15 ]
%22 = load double* %21
%23 = getelementptr inbounds [1 x %struct.__va_list_tag]* %ap, i32 0, i32 0
%24 = bitcast %struct.__va_list_tag* %23 to i8*
call void @llvm.va_end(i8* %24)
%25 = load i32* %1
ret i32 %25
}
; Function Attrs: nounwind
declare void @llvm.va_start(i8*) #1
; Function Attrs: nounwind
declare void @llvm.va_end(i8*) #1
; Function Attrs: nounwind uwtable
define i32 @main() #0 {
ret i32 0
}