LLVM IR ê 考查

目錄
  1. 結構 struct
  2. 無條仔聯合 untagged union
  3. 函數多重定義 function overloading

結構 struct

C:

#include <stdio.h>

/* 定義 struct */
struct a_struct{
  int a; // i32
  double b;
};

int main(void){
  struct a_struct a;
  return 0;
}

LLVM IR: 


; ModuleID = 'a.c'
%struct.a_struct = type { i32, double } ; 生 struct

; Function Attrs: nounwind uwtable
define i32 @main() #0 {
  %1 = alloca i32, align 4
  %a = alloca %struct.a_struct, align 8
  store i32 0, i32* %1, align 4
  ret i32 0
}

無條仔聯合 untagged union

C:

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#include <stdio.h>

union a_enum{
  int i;
  double d;
};

int main(void){
  union a_enum a;
  a.i = 9;
  return 0;
}

LLVM IR:

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%union.a_enum = type { double }

; Function Attrs: nounwind uwtable
define i32 @main() #0 {
  %1 = alloca i32, align 4
  %a = alloca %union.a_enum, align 8 ; 建立 union.a_enum type
  store i32 0, i32* %1, align 4
  %2 = bitcast %union.a_enum* %a to i32* ; 轉 union.a_enum type 到 i32
  store i32 9, i32* %2, align 8 ; 共 9 (i32) 囥入去
  ret i32 0
}



函數多重定義 function overloading

C++:

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#include <iostream>

double inc(double x){
  return x + 1.0;
};

int inc(int x){
  return x + 1;
}

int main(void){
  int a = inc(7); // inc with integer
  double b = inc(3.0); /// inc with float
  return 0;
}

LLVM IR:

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; inc double
; Function Attrs: nounwind uwtable
define double @_Z3incd(double %x) #3 {
  %1 = alloca double, align 8
  store double %x, double* %1, align 8
  %2 = load double, double* %1, align 8
  %3 = fadd double %2, 1.000000e+00
  ret double %3
}

; inc integer
; Function Attrs: nounwind uwtable
define i32 @_Z3inci(i32 %x) #3 {
  %1 = alloca i32, align 4
  store i32 %x, i32* %1, align 4
  %2 = load i32, i32* %1, align 4
  %3 = add nsw i32 %2, 1
  ret i32 %3
}

; Function Attrs: norecurse nounwind uwtable
define i32 @main() #4 {
  %1 = alloca i32, align 4
  %a = alloca i32, align 4
  %b = alloca double, align 8
  store i32 0, i32* %1, align 4
  %2 = call i32 @_Z3inci(i32 7) ; call inc integer
  store i32 %2, i32* %a, align 4
  %3 = call double @_Z3incd(double 3.000000e+00) ; call inc double
  store double %3, double* %b, align 8
  ret i32 0
}