On Wed, Nov 22, 2023 at 10:07 PM Feng Wang <[email protected]> wrote:
>
> This patch add another condition for gimple-cond optimization. Refer to
> the following test case.
> int foo1 (int data, int res)
> {
> res = data & 0xf;
> res |= res << 4;
> if (res < 0x22)
> return 0x22;
> return res;
> }
> with the compilation flag "-march=rv64gc_zba_zbb -mabi=lp64d -O2",
> before this patch the compilation result is
> foo1:
> andi a0,a0,15
> slliw a5,a0,4
> addw a3,a5,a0
> li a4,33
> add a0,a5,a0
> bleu a3,a4,.L5
> ret
> .L5:
> li a0,34
> ret
> after this patch the compilation result is
> foo1:
> andi a0,a0,15
> slliw a5,a0,4
> add a5,a5,a0
> li a0,34
> max a0,a5,a0
> ret
> The reason is in the pass_early_vrp, the arg0 of gimple_cond
> is replaced,but the PHI node still use the arg0.
> The some of evrp pass logs are as follows
> gimple_assign <mult_expr, _9, _7, 17, NULL>
> gimple_assign <nop_expr, res_5, _9, NULL, NULL>
> gimple_cond <le_expr, _9, 33, NULL, NULL>
> goto <bb 3>; [INV]
> else
> goto <bb 4>; [INV]
>
> <bb 3> :
> // predicted unlikely by early return (on trees) predictor.
>
> <bb 4> :
> # gimple_phi <_2, 34(3), res_5(2)>
> The arg0 of gimple_cond is replaced by _9,but the gimple_phi still
> uses res_5,it will cause optimization fail of PHI node to MAX_EXPR.
> So the next_use_is_phi is added to control the replacement.
I don't think this is the correct appoarch here.
We end up with the same original issue if we had wrote it like:
```
int foo1 (int data, int res)
{
res = data & 0xf;
unsigned int r = res;
r*=17;
res = r;
if (r < 0x22)
return 0x22;
return res;
}
```
I suspect instead we should extend the match.pd patterns to match this max.
We should be able to extend:
```
(for cmp (lt le gt ge eq ne)
(simplify
(cond (cmp (convert1? @1) INTEGER_CST@3) (convert2? @1) INTEGER_CST@2)
(with
```
To match instead by changing the second @1 with @4 and then using
bitwise_equal_p . If @1 != @4 but bitwise_equal_p is true, you need to
make sure the outer convert1/convert2 are nop conversions so that you
get the same extension I think ...
Note you could instead improve minmax_replacement but I have been in
the process of moving those changes to match.pd.
Thanks,
Andrew Pinski
>
> gcc/ChangeLog:
>
> * vr-values.cc (next_use_is_phi):
> (simplify_using_ranges::simplify_casted_compare):
> add new function next_use_is_phi to control the replacement.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/riscv/zbb-min-max-04.c: New test.
> ---
> gcc/testsuite/gcc.target/riscv/zbb-min-max-04.c | 14 ++++++++++++++
> gcc/vr-values.cc | 15 ++++++++++++++-
> 2 files changed, 28 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/gcc.target/riscv/zbb-min-max-04.c
>
> diff --git a/gcc/testsuite/gcc.target/riscv/zbb-min-max-04.c
> b/gcc/testsuite/gcc.target/riscv/zbb-min-max-04.c
> new file mode 100644
> index 00000000000..8c3e87a35e0
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/riscv/zbb-min-max-04.c
> @@ -0,0 +1,14 @@
> +/* { dg-do compile } */
> +/* { dg-options "-march=rv64gc_zba_zbb -mabi=lp64d" } */
> +/* { dg-skip-if "" { *-*-* } { "-O0" "-Og" } } */
> +
> +int foo1 (int data, int res)
> +{
> + res = data & 0xf;
> + res |= res << 4;
> + if (res < 0x22)
> + return 0x22;
> + return res;
> +}
> +
> +/* { dg-final { scan-assembler-times "max\t" 1 } } */
> \ No newline at end of file
> diff --git a/gcc/vr-values.cc b/gcc/vr-values.cc
> index ecb294131b0..1f7a727c638 100644
> --- a/gcc/vr-values.cc
> +++ b/gcc/vr-values.cc
> @@ -1263,6 +1263,18 @@ simplify_using_ranges::simplify_compare_using_ranges_1
> (tree_code &cond_code, tr
> return happened;
> }
>
> +/* Return true if the next use of SSA_NAME is PHI node */
> +bool
> +next_use_is_phi (tree arg)
> +{
> + use_operand_p imm = &(SSA_NAME_IMM_USE_NODE (arg));
> + use_operand_p next = imm->next;
> + if (next && next->loc.stmt
> + && (gimple_code (next->loc.stmt) == GIMPLE_PHI))
> + return true;
> + return false;
> +}
> +
> /* Simplify OP0 code OP1 when OP1 is a constant and OP0 was a SSA_NAME
> defined by a type conversion. Replacing OP0 with RHS of the type
> conversion.
> Doing so makes the conversion dead which helps subsequent passes. */
> @@ -1305,7 +1317,8 @@ simplify_using_ranges::simplify_casted_compare
> (tree_code &, tree &op0, tree &op
> if (TREE_CODE (innerop) == SSA_NAME
> && !POINTER_TYPE_P (TREE_TYPE (innerop))
> && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (innerop)
> - && desired_pro_or_demotion_p (TREE_TYPE (innerop), TREE_TYPE (op0)))
> + && desired_pro_or_demotion_p (TREE_TYPE (innerop), TREE_TYPE (op0))
> + && !next_use_is_phi (op0))
> {
> value_range vr;
>
> --
> 2.17.1
>
