[LLVMdev] Can a name in LLVM assembly language hold two types of value at the same time

[Zhongxing Xu]

I am trying to symbolically execute LLVM assembly language. I found a  
possible
semantic inconsistancy of the LLVM assembly language, or maybe my  
understanding
is wrong.

The C code is:

#include <stdlib.h>

1 int f(void)
2 {
3         int a;
4         int *b = (int *) malloc(3*sizeof(int));
5         a = 3;
6         return 0;
7 }

I compile it with llvm-gcc 4 front end. The generated LLVM assembly code  
is:

1  target endian = little
2  target pointersize = 32
3  target triple = "i686-pc-linux-gnu"

4  implementation   ; Functions:

5  int %f() {
6  entry:
7         %retval = alloca int, align 4           ; <int*> [#uses=2]
8         %tmp = alloca int, align 4              ; <int*> [#uses=2]
9         %a = alloca int, align 4                ; <int*> [#uses=1]
10        %b = alloca int*, align 4               ; <int**> [#uses=1]
11        "alloca point" = cast int 0 to int              ; <int> [#uses=0]
12        %tmp = call sbyte* %malloc( uint 12 )           ; <sbyte*>  
[#uses=1]
13        %tmp1 = cast sbyte* %tmp to int*                ; <int*>  
[#uses=1]
14        store int* %tmp1, int** %b
15        store int 3, int* %a
16        store int 0, int* %tmp
17        %tmp = load int* %tmp           ; <int> [#uses=1]
18        store int %tmp, int* %retval
19        br label %return

20 return:         ; preds = %entry
21        %retval = load int* %retval             ; <int> [#uses=1]
22        ret int %retval
23 }

declare sbyte* %malloc(uint)


After line 8, %tmp holds a pointer to stack, whose type is int*
After line 12, %tmp holds a pointer to heap, whose type is sbyte*

At line 16, value 0 is to be stored to a memory location of type int
pointed to by %tmp. But at this time %tmp is holding a pointer to
heap of type sbyte. And the heap should not be written to. (There is
no assignment to b[0] in the C code.)
So I guess that %;tmp also holds its original value, which is a pointer
to stack of type int. And we can decide which location to store according
to the type.

Could someone explain this for me? Thanks.

-- Zhongxing Xu