Re: [x86 PATCH] Double word implementation of and; cmp to not; test optimization.

[Uros Bizjak <ubizjak@gmail.com>]

On Mon, Jun 6, 2022 at 1:28 PM Uros Bizjak <ubizjak@gmail.com> wrote:
>
> On Sun, Jun 5, 2022 at 7:19 PM Roger Sayle <roger@nextmovesoftware.com> wrote:
> >
> >
> > This patch extends the recent and;cmp to not;test optimization to also
> > perform this transformation for TImode on TARGET_64BIT and DImode on -m32,
> > One motivation for this is that it's a step to fixing the current failure
> > of gcc.target/i386/pr65105-5.c on -m32.
> >
> > A more direct benefit for x86_64 is that the following code:
> >
> > int foo(__int128 x, __int128 y)
> > {
> >   return (x & y) == y;
> > }
> >
> > improves (with -O2 -mbmi) from:
> >
> >         movq    %rdi, %r8
> >         movq    %rsi, %rdi
> >         movq    %rdx, %rsi
> >         andq    %rcx, %rdi
> >         movq    %r8, %rax
> >         andq    %rdx, %rax
> >         movq    %rdi, %rdx
> >         xorq    %rsi, %rax
> >         xorq    %rcx, %rdx
> >         orq     %rdx, %rax
> >         sete    %al
> >         movzbl  %al, %eax
> >         ret
> >
> > to the much better:
> >
> >         movq    %rdi, %r8
> >         movq    %rsi, %rdi
> >         andn    %rdx, %r8, %rax
> >         andn    %rcx, %rdi, %rsi
> >         orq     %rsi, %rax
> >         sete    %al
> >         movzbl  %al, %eax
> >         ret
> >
> > The major theme of this patch is to generalize many of i386.md's
> > *di3_doubleword patterns to become *<dwi>_doubleword patterns, i.e.
> > whenever there exists a "double word" optimization for DImode with -m32,
> > there should be an equivalent TImode optimization on TARGET_64BIT.
> >
> > The following patch has been tested on x86_64-pc-linux-gnu with
> > make bootstrap and make -k check, where on TARGET_64BIT there are
> > no new failures, but paradoxically with --target_board=unix{-m32}
> > the other dg-final clause in gcc.target/i386/pr65105-5.c now fails.
> > Counter-intuitively, this is progress, and pr65105-5.c may now be
> > fixed (without using peephole2) simply by tweaking the STV pass to
> > handle andn/test (in a follow-up patch).
> > OK for mainline?
> >
> >
> > 2022-06-05  Roger Sayle  <roger@nextmovesoftware.com>
> >
> > gcc/ChangeLog
> >         * config/i386/i386.cc (ix86_rtx_costs) <COMPARE>: Provide costs
> >         for double word comparisons and tests (comparisons against zero).
> >         * config/i386/i386.md (*test<mode>_not_doubleword): Split DWI
> >         and;cmp into andn;cmp $0 as a pre-reload splitter.
> >         (define_expand and<mode>3): Generalize from SWIM1248x to SWIDWI.
> >         (define_insn_and_split "*anddi3_doubleword"): Rename/generalize...
> >         (define_insn_and_split "*and<dwi>3_doubleword"): ... to this.
> >         (define_insn "*andndi3_doubleword"): Rename and generalize...
> >         (define_insn "*andn<mode>3_doubleword): ... to this.
> >         (define_split): Split andn when TARGET_BMI for both <DWI> modes.
> >         (define_split): Split andn when !TARGET_BMI for both <DWI> modes.
> >         (define_expand <any_or><mode>3): Generalize from SWIM1248x to
> > SWIDWI.
> >         (define_insn_and_split "*<any_or><dwi>3_doubleword): Generalize
> >         from DI mode to both <DWI> modes.
> >
> > gcc/testsuite/ChangeLog
> >         * gcc.target/i386/testnot-3.c: New test case.
>
>  (define_expand "and<mode>3"
> -  [(set (match_operand:SWIM1248x 0 "nonimmediate_operand")
> -    (and:SWIM1248x (match_operand:SWIM1248x 1 "nonimmediate_operand")
> -               (match_operand:SWIM1248x 2 "<general_szext_operand>")))]
> +  [(set (match_operand:SWIDWI 0 "nonimmediate_operand")
> +    (and:SWIDWI (match_operand:SWIDWI 1 "nonimmediate_operand")
> +            (match_operand:SWIDWI 2 "<general_operand>")))]

(Didn't notice at yesterday's review)

Please do not change existing predicates, but extend
general_szext_operand mode attribute to handle TImode

-(define_insn_and_split "*anddi3_doubleword"
-  [(set (match_operand:DI 0 "nonimmediate_operand")
-    (and:DI
-     (match_operand:DI 1 "nonimmediate_operand")
-     (match_operand:DI 2 "x86_64_szext_general_operand")))
+(define_insn_and_split "*and<dwi>3_doubleword"
+  [(set (match_operand:<DWI> 0 "nonimmediate_operand")
+    (and:<DWI>
+     (match_operand:<DWI> 1 "nonimmediate_operand")
+     (match_operand:<DWI> 2 "<general_operand>")))

Also here, extended general_szext_operand attribute should handle DI and TImode.

Uros.