On Tue, Feb 14, 2017 at 11:05 AM, Bin Cheng <bin.ch...@arm.com> wrote:
> Hi,
> This is the second try fixing PR71437.  The old version patch tried to fix 
> issue in VRP but it requires further non-trivial change in VRP, specifically, 
> to better support variable value ranges.  This is not appropriate at stage 4. 
>  Alternatively, this patch tries to fix issue by improving threading.  It 
> additionally simplifies condition by using assertion conditions.
> Bootstrap and test on x86_64 and AArch64.  Is it OK?

Hmm.  So I'm not a big fan of tree_simplify_using_condition ;)  The
case in question for the PR
was an equivalent assert to the condition?  Thus basically
tree_simplify_using_condition (x <= 52, x <= 25)?

+      if (is_gimple_assign (def0)
+         && TREE_CODE (gimple_assign_rhs1 (def0)) == ASSERT_EXPR)

gimple_assign_rhs_code (def0) == ASSERT_EXPR

As you add a parameter to tree_simplify_using_condition you can as well fold
it into tree_simplify_using_condition_1.  And ideally I'd like to see us pass in
a decomposed toplevel expression to avoid

+         tree res = fold_build2 (cond_code, boolean_type_node,
+                                 assert_op0, assert_op1);

but I'm not sure that will work out ;)

So, in the end I wonder if we can fix this in threading w/o usign
(the main issue with it I have is the extensive tree building it does).


> Thanks,
> bin
> 2017-02-13  Bin Cheng  <bin.ch...@arm.com>
>         PR tree-optimization/71437
>         * tree-ssa-loop-niter.c (tree_simplify_using_condition): Only
>         expand condition if new parameter says so.  Also change it to
>         global.
>         * tree-ssa-loop-niter.h (tree_simplify_using_condition): New
>         declaration.
>         * tree-ssa-threadedge.c (tree-ssa-loop-niter.h): New include file.
>         (simplify_control_stmt_condition_1): Simplify condition using
>         assert conditions.
> gcc/testsuite/ChangeLog
> 2017-02-13  Bin Cheng  <bin.ch...@arm.com>
>         PR tree-optimization/71437
>         * gcc.dg/tree-ssa/pr71437.c: New test.

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