Re: [PATCH GCC][2/4]Simplify (cond (cmp (convert (x), c1), x, c2)) into (minmax (x, c))

[Richard Biener <richard dot guenther at gmail dot com>]

On Tue, Oct 25, 2016 at 1:21 PM, Bin Cheng <Bin.Cheng@arm.com> wrote:
> Hi,
> Second patch optimizing (cond (cmp (convert (x), c1), x, c2)) into (minmax (x, c)).  As commented in patch, this is done if:
>
> +     1) Comparison's operands are promoted from smaller type.
> +     2) Const c1 equals to c2 after canonicalizing comparison.
> +     3) Comparison has tree code LT, LE, GT or GE.
> +    This specific pattern is needed when (cmp (convert x) c) may not
> +    be simplified by comparison patterns because of multiple uses of
> +    x.  It also makes sense here because simplifying across multiple
> +    referred var is always benefitial for complicated cases.
>
> It also adds call to fold_stmt in tree-if-conv.c so that generated cond_expr statement has its chance to be simplified.

So this sounds like the fold-const.c code.  Why only for GIMPLE btw?
Thus, can you make sure you covered
all cases fold-const.c did and remove the corresponding code there?

Thanks,
Richard.

> Bootstrap and test on x86_64 and AArch64.  It introduces below failure on both x86_64 and AArch64:
> FAIL: gcc.dg/vect/slp-cond-3.c
> I believe it reveals defect in vect-slp.  In call to fold_stmt in ifcvt, canonicalization transforms _145 = _95 <= _96 ? _149 : _147 into _145 = _95 > _96 ? _147 : _149.  As a result, this stmt has different code to the first one of SLP instance.  IMO, SLP should be improved to handle operands swapping, apparently, current support is not OK.
>
> It also introduces more failures on AArch64(probably other targets) as below:
> FAIL: gcc.dg/vect/pr65947-1.c -flto -ffat-lto-objects  scan-tree-dump-times vect "LOOP VECTORIZED" 2
> FAIL: gcc.dg/vect/pr65947-1.c -flto -ffat-lto-objects  scan-tree-dump-times vect "condition expression based on integer induction." 4
> FAIL: gcc.dg/vect/pr65947-1.c scan-tree-dump-times vect "LOOP VECTORIZED" 2
> FAIL: gcc.dg/vect/pr65947-1.c scan-tree-dump-times vect "condition expression based on integer induction." 4
> FAIL: gcc.dg/vect/pr65947-13.c -flto -ffat-lto-objects  scan-tree-dump-times vect "LOOP VECTORIZED" 2
> FAIL: gcc.dg/vect/pr65947-13.c scan-tree-dump-times vect "LOOP VECTORIZED" 2
> FAIL: gcc.dg/vect/pr65947-4.c -flto -ffat-lto-objects  scan-tree-dump-times vect "LOOP VECTORIZED" 2
> FAIL: gcc.dg/vect/pr65947-4.c -flto -ffat-lto-objects  scan-tree-dump-times vect "condition expression based on integer induction." 4
> FAIL: gcc.dg/vect/pr65947-4.c scan-tree-dump-times vect "LOOP VECTORIZED" 2
> FAIL: gcc.dg/vect/pr65947-4.c scan-tree-dump-times vect "condition expression based on integer induction." 4
> FAIL: gcc.dg/vect/pr77503.c -flto -ffat-lto-objects  scan-tree-dump vect "vectorized 1 loops"
> FAIL: gcc.dg/vect/pr77503.c scan-tree-dump vect "vectorized 1 loops"
> FAIL: gcc.dg/vect/vect-pr69848.c -flto -ffat-lto-objects  scan-tree-dump vect "vectorized 1 loops"
> FAIL: gcc.dg/vect/vect-pr69848.c scan-tree-dump vect "vectorized 1 loops"
> Again, these failures reveal a defect in vectorizer that operand swapping is not supported for COND_REDUCTION.
>
> I will send another two patches independent to this patch set resolving these failures.  Is this OK?
>
> Thanks,
> bin
>
> 2016-10-21  Bin Cheng  <bin.cheng@arm.com>
>
>         * tree-if-conv.c (ifcvt_follow_ssa_use_edges): New func.
>         (predicate_scalar_phi): Call fold_stmt using the new valueize func.
>         * match.pd ((cond (cmp (convert (x), c1), x, c2)) -> (minmax (x, c))):
>         New pattern.
>
> gcc/testsuite/ChangeLog
> 2016-10-21  Bin Cheng  <bin.cheng@arm.com>
>
>         * gcc.dg/fold-condcmpconv-1.c: New test.
>         * gcc.dg/fold-condcmpconv-2.c: New test.