Richard Biener <rguent...@suse.de> writes: > 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.
Yeah. I think the problem in this case is that the step is variable. So if we only supported PLUS_EXPRs, we'd need a separate NEGATE_EXPR stmt (which presumably would be folded in later). Thanks, Richard
