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[tree-ssa] Simplifying TARGET_EXPR
- From: Jason Merrill <jason at redhat dot com>
- To: gcc at gcc dot gnu dot org
- Date: Tue, 16 Jul 2002 11:02:01 +0100
- Subject: [tree-ssa] Simplifying TARGET_EXPR
Thinking about simplifying TARGET_EXPR, I see two issues to be dealt with:
1) expand_expr's treatment of TARGET_EXPR depends on whether or not it is
being expanded with a target: if so, it initializes the target object;
if not, it initializes a new object. There's no way to model that
behavior with the current simplification code, as there's no concept
of 'target'.
However, I think that the copy-elision should only occur under an
INIT_EXPR, so we can check for TARGET_EXPR in simplify_modify_expr.
This should work fine.
2) Passing a TARGET_EXPR to a call means initializing the temporary on the
stack and passing its address to the call. There's no way to express
this in a simplified form; if we replace the TARGET_EXPR with the
variable it initializes, expand_call will make a bitwise copy, which is
wrong. I can think of two solutions to this:
a) Change expand_call to not copy variables with DECL_ARTIFICIAL set.
b) Pass an ADDR_EXPR of the variable instead, and change expand_call
to handle that case.
My preference is for (b), as (a) might have unintended consequences.
Thoughts?
Jason