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On 04/06/11 12:53, kevin diggs wrote:
> Hi,
>
> Sorry for the noise. I am trying to learn RTL. A simple function's
> PowerPC RTL (gcc 3.4.6) has as one of the first RTL expressions:
>
> (insn 3 2 4 (set (mem/f:SI (reg/f:SI 114 virtual-stack-vars) [0 u+0 S4 A32])
> (reg:SI 3 3 [ u ])) -1 (nil)
> (nil))
>
> From the gcc-int manual, the first 3 fields (arguments) are:
>
> 1) unique id
> 2) previous instruction chain
> 3) next instruction chain
>
> The last four are: RTL expression for the side effect (pattern),
> instruction code of match (-1 if not yet matched), dependent
> instruction list, and note list.
>
> So for this example (which I *think* is putting the register argument
> (PowerPC ABI?) on the stack???):
>
> 1) 3
> 2) 2
> 3) 4
> 5) (set (mem/f:SI (reg/f:SI 114 virtual-stack-vars) [0 u+0 S4 A32])
> (reg:SI 3 3 [u]) )
> 6) -1
> 7) (nil)
> 8) (nil)
>
> I am having trouble reading the pattern (field 5). It is a set:
>
> (set lval x)
>
> Two arguments, in this case the address is a mem:
>
> (mem/f:SI ...)
>
> and the source (x) is a reg:
>
> (reg:SI 3 3 [u])
>
> A mem has two arguments:
>
> (mem:m addr alias)
>
> The addr appears to be a reg but regs only have one argument? What is
> "virtual-stack-vars"? Is the stuff in square brackets the alias set?
> It's a vector (list?), right?
>
> The 'x' in the set is "(reg:SI 3 3 [u])". What is the second '3' and
> the '[u]'???
A lot of this is covered in the GCC internals documentation.
Personally, I just look at the texi source rather than the formatted
texinfo blobs.
@findex MEM_POINTER
@cindex @code{mem} and @samp{/f}
@cindex @code{frame_related}, in @code{mem}
@item MEM_POINTER (@var{x})
Nonzero in a @code{mem} if the memory reference holds a pointer.
Stored in the @code{frame_related} field and printed as @samp{/f}.
The second "3" is the register's name. Apparently hard reg 3 has no
convenient pseudo name on your target. The "u" is the REG_EXPR:
@findex REG_EXPR
@item REG_EXPR (@var{x})
If this register is known to hold the value of some user-level
declaration, this is that tree node.
virtual-stack-vars is a special pseudo used to reference objects in the
stack. Again, I would refer you to the rtl.texi documentation which
discusses the various virtual registers in more detail.
@findex VIRTUAL_STACK_VARS_REGNUM
@cindex @code{FRAME_GROWS_DOWNWARD} and virtual registers
@item VIRTUAL_STACK_VARS_REGNUM
If @code{FRAME_GROWS_DOWNWARD} is defined to a nonzero value, this points
to immediately above the first variable on the stack. Otherwise, it points
to the first variable on the stack.
@cindex @code{STARTING_FRAME_OFFSET} and virtual registers
@cindex @code{FRAME_POINTER_REGNUM} and virtual registers
@code{VIRTUAL_STACK_VARS_REGNUM} is replaced with the sum of the
register given by @code{FRAME_POINTER_REGNUM} and the value
@code{STARTING_FRAME_OFFSET}.
jeff
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