[gcc r11-5766] VAX: Correct fatal issues with the `ffs' builtin

[Maciej W. Rozycki <macro@gcc.gnu.org>]

https://gcc.gnu.org/g:8c18e22afb061329766be3532a06a85ccc492d9c

commit r11-5766-g8c18e22afb061329766be3532a06a85ccc492d9c
Author: Maciej W. Rozycki <macro@linux-mips.org>
Date:   Sat Dec 5 18:26:24 2020 +0000

    VAX: Correct fatal issues with the `ffs' builtin
    
    The `builtins.md' machine description fragment is not included anywhere
    and is therefore dead code, which has become bitrotten due to non-use.
    
    If actually enabled, it does not build due to the use of an unknown `t'
    constraint:
    
    .../gcc/config/vax/builtins.md:42:1: error: undefined machine-specific constraint at this point: "t"
    .../gcc/config/vax/builtins.md:42:1: note:  in operand 1
    
    which came from commit becb93d02cc1 ("builtins.md (ffssi2_internal):
    Correct constraint."), which was not applied as posted and reviewed; `T'
    was meant to be used instead.
    
    Once this has been fixed this code still fails building:
    
    .../gcc/config/vax/builtins.md: In function 'rtx_def* gen_ffssi2(rtx, rtx)':
    .../gcc/config/vax/builtins.md:35:19: error: 'gen_bne' was not declared in this
    scope; did you mean 'gen_use'?
       35 |   emit_jump_insn (gen_bne (label));
          |                   ^~~~~~~
          |                   gen_use
    make[2]: *** [Makefile:1122: insn-emit.o] Error 1
    
    Finally the FFS machine instruction sets the Z condition code according
    to the comparison of the value held in the source operand against zero
    rather than the value held in the target operand.  If the source operand
    is found hold zero, then the target operand is set to the width of the
    source operand, 32 for SImode (FFS supports arbitrary widths).
    
    Correct the build issues then and update RTL to match the operation of
    the machine instruction.  A test case will be added separately.
    
            gcc/
            * config/vax/builtins.md (ffssi2): Make preparation statements
            actually buildable.
            (ffssi2_internal): Fix input constraints; make the RTL pattern
            match reality for `cc0'.

Diff:
---
 gcc/config/vax/builtins.md | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/gcc/config/vax/builtins.md b/gcc/config/vax/builtins.md
index ac0e0271ddd..6bce7a85add 100644
--- a/gcc/config/vax/builtins.md
+++ b/gcc/config/vax/builtins.md
@@ -31,8 +31,12 @@
   "
 {
   rtx label = gen_label_rtx ();
+  rtx label_ref = gen_rtx_LABEL_REF (VOIDmode, label);
+  rtx cond = gen_rtx_NE (VOIDmode, cc0_rtx, const0_rtx);
+  rtx target = gen_rtx_IF_THEN_ELSE (VOIDmode, cond, label_ref, pc_rtx);
+
   emit_insn (gen_ffssi2_internal (operands[0], operands[1]));
-  emit_jump_insn (gen_bne (label));
+  emit_jump_insn (gen_rtx_SET (pc_rtx, target));
   emit_insn (gen_negsi2 (operands[0], const1_rtx));
   emit_label (label);
   emit_insn (gen_addsi3 (operands[0], operands[0], const1_rtx));
@@ -41,8 +45,10 @@
 
 (define_insn "ffssi2_internal"
   [(set (match_operand:SI 0 "nonimmediate_operand" "=rQ")
-	(ffs:SI (match_operand:SI 1 "general_operand" "nrQt")))
-   (set (cc0) (match_dup 0))]
+	(ffs:SI (match_operand:SI 1 "general_operand" "nrQT")))
+   (set (cc0)
+	(compare (match_dup 1)
+		 (const_int 0)))]
   ""
   "ffs $0,$32,%1,%0")