[gcc(refs/users/meissner/heads/work235-sha)] PR target/117251: Improve vector nor to vector nand fusion

[Michael Meissner]

https://gcc.gnu.org/g:3d4e0ea21badae4c3088cb5eb32f5dcfaaa3fc08

commit 3d4e0ea21badae4c3088cb5eb32f5dcfaaa3fc08
Author: Michael Meissner <meissner@linux.ibm.com>
Date:   Fri Jan 30 17:06:23 2026 -0500

    PR target/117251: Improve vector nor to vector nand fusion
    
    See the following post for a complete explanation of what the patches
    for PR target/117251:
    
     * https://gcc.gnu.org/pipermail/gcc-patches/2025-June/686474.html
    
    This is patch #40 of 45 to generate the 'XXEVAL' instruction on power10
    and power11 instead of using the Altivec 'VNOR' instruction feeding
    into 'VNAND'.  The 'XXEVAL' instruction can use all 64 vector
    registers, instead of the 32 registers that traditional Altivec vector
    instructions use.  By allowing all of the vector registers to be used,
    it reduces the amount of spilling that a large benchmark generated.
    
    Currently the following code:
    
            vector int a, b, c, d;
            a = ~ ((~ (c | d)) & b);
    
    Generates:
    
            vnor   t,c,d
            vnand  a,t,b
    
    Now in addition with this patch, if the arguments or result is
    allocated to a traditional FPR register, the GCC compiler will now
    generate the following code instead of adding vector move instructions:
    
            xxeval a,b,c,247
    
    Since fusion using 2 Altivec instructions is slightly faster than using
    the 'XXEVAL' instruction we prefer to generate the Altivec instructions
    if we can.  In addition, because 'XXEVAL' is a prefixed instruction, it
    possibly might generate an extra NOP instruction to align the 'XXEVAL'
    instruction.
    
    I have tested these patches on both big endian and little endian
    PowerPC servers, with no regressions.  Can I check these patchs into
    the trunk?
    
    2026-01-30  Michael Meissner  <meissner@linux.ibm.com>
    
    gcc/
    
            PR target/117251
            * config/rs6000/fusion.md: Regenerate.
            * config/rs6000/genfusion.pl (gen_logical_addsubf): Add support
            to generate vector nor => nand fusion if XXEVAL is supported.

Diff:
---
 gcc/config/rs6000/fusion.md    | 15 +++++++++------
 gcc/config/rs6000/genfusion.pl |  1 +
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/gcc/config/rs6000/fusion.md b/gcc/config/rs6000/fusion.md
index 2d355c435b29..11c1d95dc110 100644
--- a/gcc/config/rs6000/fusion.md
+++ b/gcc/config/rs6000/fusion.md
@@ -2414,20 +2414,23 @@
 ;; logical-logical fusion pattern generated by gen_logical_addsubf
 ;; vector vnor -> vnand
 (define_insn "*fuse_vnor_vnand"
-  [(set (match_operand:VM 3 "altivec_register_operand" "=&0,&1,&v,v")
-        (ior:VM (not:VM (and:VM (not:VM (match_operand:VM 0 "altivec_register_operand" "v,v,v,v"))
-                          (not:VM (match_operand:VM 1 "altivec_register_operand" "v,v,v,v"))))
-                 (not:VM (match_operand:VM 2 "altivec_register_operand" "v,v,v,v"))))
-   (clobber (match_scratch:VM 4 "=X,X,X,&v"))]
+  [(set (match_operand:VM 3 "vector_fusion_operand" "=&0,&1,&v,wa,v")
+        (ior:VM (not:VM (and:VM (not:VM (match_operand:VM 0 "vector_fusion_operand" "v,v,v,wa,v"))
+                          (not:VM (match_operand:VM 1 "vector_fusion_operand" "v,v,v,wa,v"))))
+                 (not:VM (match_operand:VM 2 "vector_fusion_operand" "v,v,v,wa,v"))))
+   (clobber (match_scratch:VM 4 "=X,X,X,X,&v"))]
   "(TARGET_P10_FUSION)"
   "@
    vnor %3,%1,%0\;vnand %3,%3,%2
    vnor %3,%1,%0\;vnand %3,%3,%2
    vnor %3,%1,%0\;vnand %3,%3,%2
+   xxeval %x3,%x2,%x1,%x0,247
    vnor %4,%1,%0\;vnand %3,%4,%2"
   [(set_attr "type" "fused_vector")
    (set_attr "cost" "6")
-   (set_attr "length" "8")])
+   (set_attr "length" "8")
+   (set_attr "prefixed" "*,*,*,yes,*")
+   (set_attr "isa" "*,*,*,xxeval,*")])
 
 ;; logical-logical fusion pattern generated by gen_logical_addsubf
 ;; vector vor -> vnand
diff --git a/gcc/config/rs6000/genfusion.pl b/gcc/config/rs6000/genfusion.pl
index 9ba1ed618dee..73111836a319 100755
--- a/gcc/config/rs6000/genfusion.pl
+++ b/gcc/config/rs6000/genfusion.pl
@@ -254,6 +254,7 @@ sub gen_logical_addsubf
       "vnand_vnand" => 241,
       "vorc_vnand"  => 244,
       "veqv_vnand"  => 246,
+      "vnor_vnand"  => 247,
     );
 
     KIND: foreach $kind ('scalar','vector') {