On Wed, Aug 6, 2025 at 7:30 PM Andrew Pinski <quic_apin...@quicinc.com> wrote:
>
> While looking into the gimple level after optimization of the highway code
> from google, I noticed in .optimized we still have:
> ```
> MEM <vector(8) short int> [(short int *)&a] = { 0, 0, 0, 0, 0, 0, 0, 0 };
> D.4398 = a;
> a ={v} {CLOBBER(eos)};
> D.4389 = D.4398;
> D.4390 = D.4389;
> D.4361 = D.4390;
> D.4195 = D.4361;
> return D.4195;
> ```
> Note this is with SRA disabled since I noticed there is better code
> generation with
> SRA disabled but that is a different story and I will get to that later on.
>
> Which could be just optimized to a single store of `{}` .
>
> The reason why the optimize_agr_copyprop does not handle the above is there
> was clobbers
> inbetween the store in the last forwprop pass and currently don't copy after
> the first use.
> While optimize_aggr_zeroprop does handle copying over clobbers just fine.
>
> So this allows the recognization of the store to a to be like a memset to
> optimize_aggr_zeroprop
> and then the result just falls through.
>
> Bootstrapped and tested on x86_64-linux-gnu.
>
> gcc/ChangeLog:
>
> * tree-ssa-forwprop.cc (optimize_aggr_zeroprop): Recognize stores
> of integer_zerop as memset of 0.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/torture/copy-prop-aggr-zero-1.c: New test.
> * gcc.dg/torture/copy-prop-aggr-zero-2.c: New test.
> * gcc.dg/tree-ssa/copy-prop-aggregate-zero-1.c: New test.
> * gcc.dg/tree-ssa/copy-prop-aggregate-zero-2.c: New test.
> * gcc.dg/tree-ssa/copy-prop-aggregate-zero-3.c: New test.
>
> Signed-off-by: Andrew Pinski <quic_apin...@quicinc.com>
> ---
> .../gcc.dg/torture/copy-prop-aggr-zero-1.c | 28 +++++++++++++++++++
> .../gcc.dg/torture/copy-prop-aggr-zero-2.c | 28 +++++++++++++++++++
> .../tree-ssa/copy-prop-aggregate-zero-1.c | 28 +++++++++++++++++++
> .../tree-ssa/copy-prop-aggregate-zero-2.c | 25 +++++++++++++++++
> .../tree-ssa/copy-prop-aggregate-zero-3.c | 25 +++++++++++++++++
> gcc/tree-ssa-forwprop.cc | 15 ++++++++++
> 6 files changed, 149 insertions(+)
> create mode 100644 gcc/testsuite/gcc.dg/torture/copy-prop-aggr-zero-1.c
> create mode 100644 gcc/testsuite/gcc.dg/torture/copy-prop-aggr-zero-2.c
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/copy-prop-aggregate-zero-1.c
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/copy-prop-aggregate-zero-2.c
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/copy-prop-aggregate-zero-3.c
>
> diff --git a/gcc/testsuite/gcc.dg/torture/copy-prop-aggr-zero-1.c
> b/gcc/testsuite/gcc.dg/torture/copy-prop-aggr-zero-1.c
> new file mode 100644
> index 00000000000..5c457b9bc2f
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/torture/copy-prop-aggr-zero-1.c
> @@ -0,0 +1,28 @@
> +/* { dg-do run } */
> +
> +/* Make sure a bit-field store of 0 cause the whole assignment become 0. */
> +
> +struct s1
> +{
> + unsigned char c:1;
> + unsigned char d:7;
> +};
> +
> +__attribute__((noinline))
> +struct s1 f(struct s1 a)
> +{
> + a.c = 0;
> + struct s1 t = a;
> + return t;
> +}
> +
> +int main()
> +{
> + struct s1 a = {1, 2};
> + struct s1 b = f(a);
> + if (b.c != 0)
> + __builtin_abort();
> + if (b.d != 2)
> + __builtin_abort();
> + return 0;
> +}
> diff --git a/gcc/testsuite/gcc.dg/torture/copy-prop-aggr-zero-2.c
> b/gcc/testsuite/gcc.dg/torture/copy-prop-aggr-zero-2.c
> new file mode 100644
> index 00000000000..f1da1615e8e
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/torture/copy-prop-aggr-zero-2.c
> @@ -0,0 +1,28 @@
> +/* { dg-do run } */
> +
> +/* Make sure a bit-field store of 0 cause the whole assignment become 0. */
> +
> +struct s1
> +{
> + unsigned char d:7;
> + unsigned char c:1;
> +};
> +
> +__attribute__((noinline))
> +struct s1 f(struct s1 a)
> +{
> + a.c = 0;
> + struct s1 t = a;
> + return t;
> +}
> +
> +int main()
> +{
> + struct s1 a = {2, 1};
> + struct s1 b = f(a);
> + if (b.c != 0)
> + __builtin_abort();
> + if (b.d != 2)
> + __builtin_abort();
> + return 0;
> +}
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/copy-prop-aggregate-zero-1.c
> b/gcc/testsuite/gcc.dg/tree-ssa/copy-prop-aggregate-zero-1.c
> new file mode 100644
> index 00000000000..577a5b5817c
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/copy-prop-aggregate-zero-1.c
> @@ -0,0 +1,28 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O1 -fno-tree-sra -fdump-tree-optimized
> -fdump-tree-forwprop1-details" } */
> +
> +extern void link_error (void);
> +
> +/* Check for copyprop on structs with zeroing. */
> +#define vector16 __attribute__((vector_size(64)))
> +
> +struct g
> +{
> + vector16 unsigned char t;
> +};
> +
> +struct g f(void)
> +{
> + struct g temp_struct1 ;
> + temp_struct1.t = (vector16 unsigned char){};
> + struct g temp_struct2 = temp_struct1;
> + struct g temp_struct3 = temp_struct2;
> + struct g temp_struct4 = temp_struct3;
> + return temp_struct4;
> +}
> +
> +/* There should be no references to any of "temp_struct*"
> + temporaries. */
> +/* { dg-final { scan-tree-dump-times "temp_struct" 0 "optimized" } } */
> +/* Also check that forwprop pass did the copy prop. */
> +/* { dg-final { scan-tree-dump-times "after previous" 4 "forwprop1" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/copy-prop-aggregate-zero-2.c
> b/gcc/testsuite/gcc.dg/tree-ssa/copy-prop-aggregate-zero-2.c
> new file mode 100644
> index 00000000000..ce3c6129b1a
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/copy-prop-aggregate-zero-2.c
> @@ -0,0 +1,25 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O1 -fno-tree-sra -fdump-tree-optimized
> -fdump-tree-forwprop1-details" } */
> +
> +extern void link_error (void);
> +
> +struct g
> +{
> + unsigned int t;
> +};
> +
> +struct g f(void)
> +{
> + struct g temp_struct1 ;
> + temp_struct1.t = 0;
> + struct g temp_struct2 = temp_struct1;
> + struct g temp_struct3 = temp_struct2;
> + struct g temp_struct4 = temp_struct3;
> + return temp_struct4;
> +}
> +
> +/* There should be no references to any of "temp_struct*"
> + temporaries. */
> +/* { dg-final { scan-tree-dump-times "temp_struct" 0 "optimized" } } */
> +/* Also check that forwprop pass did the copy prop. */
> +/* { dg-final { scan-tree-dump-times "after previous" 4 "forwprop1" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/copy-prop-aggregate-zero-3.c
> b/gcc/testsuite/gcc.dg/tree-ssa/copy-prop-aggregate-zero-3.c
> new file mode 100644
> index 00000000000..94ce965e7ce
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/copy-prop-aggregate-zero-3.c
> @@ -0,0 +1,25 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O1 -fno-tree-sra -fdump-tree-optimized
> -fdump-tree-forwprop1-details" } */
> +
> +extern void link_error (void);
> +
> +struct g
> +{
> + _Complex unsigned int t;
> +};
> +
> +struct g f(void)
> +{
> + struct g temp_struct1 ;
> + temp_struct1.t = 0;
> + struct g temp_struct2 = temp_struct1;
> + struct g temp_struct3 = temp_struct2;
> + struct g temp_struct4 = temp_struct3;
> + return temp_struct4;
> +}
> +
> +/* There should be no references to any of "temp_struct*"
> + temporaries. */
> +/* { dg-final { scan-tree-dump-times "temp_struct" 0 "optimized" } } */
> +/* Also check that forwprop pass did the copy prop. */
> +/* { dg-final { scan-tree-dump-times "after previous" 4 "forwprop1" } } */
> diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
> index 3d38d88844b..1cde5f85150 100644
> --- a/gcc/tree-ssa-forwprop.cc
> +++ b/gcc/tree-ssa-forwprop.cc
> @@ -1340,6 +1340,21 @@ optimize_aggr_zeroprop (gimple_stmt_iterator *gsip)
> }
> }
> }
> + /* A store of integer (scalar, vector or complex) zeros is
> + a zero store. */
> + else if (gimple_store_p (stmt)
> + && gimple_assign_single_p (stmt)
> + && integer_zerop (gimple_assign_rhs1 (stmt)))
Do we do the correct things for bitfield stores or should we restrict
this to mode-size or BLKmode types?
> + {
> + tree rhs = gimple_assign_rhs1 (stmt);
> + tree type = TREE_TYPE (rhs);
> + dest = gimple_assign_lhs (stmt);
> + ao_ref_init (&read, dest);
> + /* For integral types, the type precision needs to be a multiply of
> BITS_PER_UNIT. */
> + if (INTEGRAL_TYPE_P (type)
> + && (TYPE_PRECISION (type) % BITS_PER_UNIT) != 0)
> + dest = NULL_TREE;
> + }
> else if (gimple_store_p (stmt)
> && gimple_assign_single_p (stmt)
> && TREE_CODE (gimple_assign_rhs1 (stmt)) == CONSTRUCTOR
> --
> 2.43.0
>
