That looks like a bug. Only happens on CPUX architectures. If you open up
a ticket on https://sourceforge.net/p/mspgcc/bugs/ I may be able to look at
it some time.
Peter
On Wed, Jul 3, 2013 at 7:37 AM, Daniele Alessandrelli <
daniele.alessandre...@gmail.com> wrote:
> Hi everybody,
>
> I noticed a strange behavior when executing certain shift operations and I
> wonder whether this is because of a compiler bug or just my ignorance in
> low-level C.
>
> For example, when compiling (with no optimization) and then executing the
> following lines of code the result I obtain is 16 instead of 64:
>
> uint32_t u32_var;
>
> int main(void)
> {
> int tmp;
> ...
> u32_var = 0xa;
> tmp = 16 << (u32_var & 0x07);
> printf("tmp: %d\n", tmp);
> ...
> }
>
> However, if I change the type of tmp form "int" to "unsigned int" the
> result is correct (i.e., 64).
>
> This is assembly code generated when tmp is defined as int (i.e., when the
> result is wrong).
>
> 5c44: b2 40 0a 00 mov #10, &0x1c02 ;#0x000a
>
> 5c48: 02 1c
>
> 5c4a: 82 43 04 1c mov #0, &0x1c04 ;r3 As==00
>
> 5c4e: 1e 42 02 1c mov &0x1c02,r14
>
> 5c52: 1f 42 04 1c mov &0x1c04,r15
>
> 5c56: 0f 4e mov r14, r15
>
> 5c58: 3f f0 07 00 and #7, r15 ;#0x0007
>
> 5c5c: 3e 40 10 00 mov #16, r14 ;#0x0010
>
> 5c60: 4f 4f mov.b r15, r15
>
> 5c62: 7f f0 0f 00 and.b #15, r15 ;#0x000f
>
> 5c66: 84 4e fc ff mov r14, -4(r4) ;0xfffc(r4)
>
> 5c6a: 4f 93 tst.b r15
>
> 5c6c: 03 24 jz $+8 ;abs 0x5c74
>
> 5c6e: 7f 53 add.b #-1, r15 ;r3 As==11
>
> 5c70: cf 18 0e 5e .rpt r15
>
> addx r14, r14
>
> 5c74: 14 12 fc ff push -4(r4) ;0xfffc(r4)
>
> 5c78: 30 12 9a 66 push #26266 ;#0x669a
>
> 5c7c: b0 12 ae 5c call #0x5cae
>
>
> As you can see, at address 0x5c66, register 14 (containing 16) is stored in
> memory before being shifted. The stored valued (i.e., 16) is then pushed in
> the stack (i.e., passed as an argument to the printf() function).
>
> I have a similar problem also when using -Os, but I can't replicate it with
> simple code because of the optimization. However, if needed, I can post the
> (large) source code that is giving me this problem.
>
> The version of msp430-gcc that I am using is:
> msp430-gcc (GCC) 4.7.0 20120322 (mspgcc dev 20120911)
>
> Thank you for any help you can provide.
>
> Regards.
>
> Daniele
>
>
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