On Mon, 23 Sep 2024, Artemiy Volkov wrote:
> Implement a match.pd transformation inverting the sign of X in
> C1 - X cmp C2, where C1 and C2 are integer constants and X is
> of a wrapping signed type, by observing that:
>
> (a) If cmp is == or !=, simply move X and C2 to opposite sides of
> the comparison to arrive at X cmp C1 - C2.
>
> (b) If cmp is <:
> - C1 - X < C2 means that C1 - X spans the values of -INF,
> -INF + 1, ..., C2 - 1;
> - Therefore, X is one of C1 - -INF, C1 - (-INF + 1), ...,
> C1 - C2 + 1;
> - Subtracting (C1 + 1), X - (C1 + 1) is one of - (-INF) - 1,
> - (-INF) - 2, ..., -C2;
> - Using the fact that - (-INF) - 1 is +INF, derive that
> X - (C1 + 1) spans the values +INF, +INF - 1, ..., -C2;
> - Thus, the original expression can be simplified to
> X - (C1 + 1) > -C2 - 1.
>
> (c) Similarly, C1 - X <= C2 is equivalent to X - (C1 + 1) >= -C2 - 1.
>
> (d) The >= and > cases are negations of (b) and (c), respectively.
>
> (e) In all cases, the expression -C2 - 1 can be shortened to
> bit_not (C2).
>
> This transformation allows to occasionally save load-immediate /
> subtraction instructions, e.g. the following statement:
>
> 10 - (int)f() >= 20;
>
> now compiles to
>
> addi a0,a0,-11
> slti a0,a0,-20
>
> instead of
>
> li a5,10
> sub a0,a5,a0
> slti t0,a0,20
> xori a0,t0,1
>
> on 32-bit RISC-V when compiled with -fwrapv.
>
> Additional examples can be found in the newly added test file. This
> patch has been bootstrapped and regtested on aarch64, x86_64, and i386,
> and additionally regtested on riscv32.
>
> gcc/ChangeLog:
>
> PR tree-optimization/116024
> * match.pd: New transformation around integer comparison.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/tree-ssa/pr116024-1-fwrapv.c: New test.
>
> Signed-off-by: Artemiy Volkov <arte...@synopsys.com>
> ---
> gcc/match.pd | 20 ++++-
> .../gcc.dg/tree-ssa/pr116024-1-fwrapv.c | 73 +++++++++++++++++++
> 2 files changed, 92 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr116024-1-fwrapv.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index d0489789527..bf3b4a2e3fe 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -8970,7 +8970,25 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> (cmp (plus @1 (minus @2 @0)) @2))
> (if (cmp == LT_EXPR || cmp == GE_EXPR)
> (cmp (plus @1 (minus @2
> - (plus @0 { build_one_cst (TREE_TYPE (@1)); }))) @2)))))))
> + (plus @0 { build_one_cst (TREE_TYPE (@1)); }))) @2)))
> +/* For wrapping signed types (-fwrapv), transform like so (using < as
> example):
> + C1 - X < C2
> + ==> C1 - X = { -INF, -INF + 1, ..., C2 - 1 }
> + ==> X = { C1 - (-INF), C1 - (-INF + 1), ..., C1 - C2 + 1 }
> + ==> X - (C1 + 1) = { - (-INF) - 1, - (-INF) - 2, ..., -C2 }
> + ==> X - (C1 + 1) = { +INF, +INF - 1, ..., -C2 }
> + ==> X - (C1 + 1) > -C2 - 1
> + ==> X - (C1 + 1) > bit_not (C2)
> +
> + Similarly,
> + C1 - X <= C2 ==> X - (C1 + 1) >= bit_not (C2);
> + C1 - X >= C2 ==> X - (C1 + 1) <= bit_not (C2);
> + C1 - X > C2 ==> X - (C1 + 1) < bit_not (C2). */
> + (if (TYPE_OVERFLOW_WRAPS (TREE_TYPE (@1)))
You need to add && !TYPE_UNSIGNED (TREE_TYPE (@1)) here,
TYPE_OVERFLOW_WRAPS is also true for unsigned types.
OK with that change.
Thanks,
Richard.
> + (if (cmp == EQ_EXPR || cmp == NE_EXPR)
> + (cmp @1 (minus @0 @2))
> + (rcmp (minus @1 (plus @0 { build_one_cst (TREE_TYPE (@1)); }))
> + (bit_not @2))))))))
>
> /* Canonicalizations of BIT_FIELD_REFs. */
>
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr116024-1-fwrapv.c
> b/gcc/testsuite/gcc.dg/tree-ssa/pr116024-1-fwrapv.c
> new file mode 100644
> index 00000000000..c2bf1d17234
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr116024-1-fwrapv.c
> @@ -0,0 +1,73 @@
> +/* PR tree-optimization/116024 */
> +/* { dg-do compile } */
> +/* { dg-options "-O1 -fdump-tree-forwprop1-details -fwrapv" } */
> +
> +#include <stdint.h>
> +
> +uint32_t f(void);
> +
> +int32_t i2(void)
> +{
> + int32_t l = 2;
> + l = 10 - (int32_t)f();
> + return l <= 20; // f() - 11 >= -21
> +}
> +
> +int32_t i2a(void)
> +{
> + int32_t l = 2;
> + l = 10 - (int32_t)f();
> + return l < 30; // f() - 11 > -31
> +}
> +
> +int32_t i2b(void)
> +{
> + int32_t l = 2;
> + l = 200 - (int32_t)f();
> + return l <= 100; // f() - 201 >= -101
> +}
> +
> +int32_t i2c(void)
> +{
> + int32_t l = 2;
> + l = 300 - (int32_t)f();
> + return l < 100; // f() - 301 > -101
> +}
> +
> +int32_t i2d(void)
> +{
> + int32_t l = 2;
> + l = 1000 - (int32_t)f();
> + return l >= 2000; // f() - 1001 <= -2001
> +}
> +
> +int32_t i2e(void)
> +{
> + int32_t l = 2;
> + l = 1000 - (int32_t)f();
> + return l > 3000; // f() - 1001 < -3001
> +}
> +
> +int32_t i2f(void)
> +{
> + int32_t l = 2;
> + l = 20000 - (int32_t)f();
> + return l >= 10000; // f() - 20001 <= -10001
> +}
> +
> +int32_t i2g(void)
> +{
> + int32_t l = 2;
> + l = 30000 - (int32_t)f();
> + return l > 10000; // f() - 30001 < -10001
> +}
> +
> +/* { dg-final { scan-tree-dump-times "Removing dead stmt:.*?- _" 8
> "forwprop1" } } */
> +/* { dg-final { scan-tree-dump-times "gimple_simplified to.* \\+ -11.*\n.*>=
> -21" 1 "forwprop1" } } */
> +/* { dg-final { scan-tree-dump-times "gimple_simplified to.* \\+ -11.*\n.*>=
> -30" 1 "forwprop1" } } */
> +/* { dg-final { scan-tree-dump-times "gimple_simplified to.* \\+
> -201.*\n.*>= -101" 1 "forwprop1" } } */
> +/* { dg-final { scan-tree-dump-times "gimple_simplified to.* \\+
> -301.*\n.*>= -100" 1 "forwprop1" } } */
> +/* { dg-final { scan-tree-dump-times "gimple_simplified to.* \\+
> -1001.*\n.*< -2000" 1 "forwprop1" } } */
> +/* { dg-final { scan-tree-dump-times "gimple_simplified to.* \\+
> -1001.*\n.*< -3001" 1 "forwprop1" } } */
> +/* { dg-final { scan-tree-dump-times "gimple_simplified to.* \\+
> -20001.*\n.*< -10000" 1 "forwprop1" } } */
> +/* { dg-final { scan-tree-dump-times "gimple_simplified to.* \\+
> -30001.*\n.*< -10001" 1 "forwprop1" } } */
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
