Should embedded systems compilers be trusted

There are a few guarantees I exploit in the C Standard. For instance,
I might write

    (unsigned)-1

to get the maximum value for an unsigned integer.

Also, I might rely on things such as:

    memset(data,-1,sizeof data)

to set all bits in a chunk of memory to 1.

I'm using an embedded systems compiler now though and I'm hesitant to
trust it with things like this. I've already come across the following
quirks:

1) You can't define a variable as const unless it can be put in the
chip's ROM.
2) There's no stack used by default; you must define a function as
"reentrant" if you want a stack.

To the people here who have experience with embedded systems C
compilers, how do you feel about trusting its C compliance? Some
issues I'd be concerned about are:

1) int being at least 16-Bit
2) long being at least 32-Bit
3) Compliant conversion between signed and unsigned types

I'm using the PIC C compiler to program the PIC16F684 chip.