On Tue, 25 Apr 2023, Richard Sandiford wrote: > juzhe.zh...@rivai.ai writes: > > diff --git a/gcc/tree-ssa-loop-manip.cc b/gcc/tree-ssa-loop-manip.cc > > index a52277abdbf..54845a62298 100644 > > --- a/gcc/tree-ssa-loop-manip.cc > > +++ b/gcc/tree-ssa-loop-manip.cc > > @@ -59,14 +59,14 @@ static bitmap_obstack loop_renamer_obstack; > > void > > create_iv (tree base, tree step, tree var, class loop *loop, > > gimple_stmt_iterator *incr_pos, bool after, > > - tree *var_before, tree *var_after) > > + tree *var_before, tree *var_after, enum tree_code code) > > The comment needs to be updated to describe the new interface. > > This is personal preference, but: I think the interface would be > clearer if the code argument came between the base and step, > so that the order matches a SCEV. The code could no longer be > a default argument, and so all callers would need to be updated, > but IMO that's OK. Not sure what others think though.
Just a quick comment - I think decrementing IVs are already supported, you just have to make 'step' negative (or large positive). If you really think using MINUS_EXPR is better or even required for VLA step please add an assert that 'code' is either PLUS_EXPR or MINUS_EXPR. Note that for INTEGER_CST step we rewrite x - CST to x + -CST during folding. Going over v3 now. Richard.
