[gcc r17-3470] vect: fixup divmod pattern [PR126961]

https://gcc.gnu.org/g:fc58b1fc537f0b8cad5762f70809678d22dd3c80

commit r17-3470-gfc58b1fc537f0b8cad5762f70809678d22dd3c80
Author: Tamar Christina <[email protected]>
Date:   Thu Aug 20 12:54:39 2026 +0100

    vect: fixup divmod pattern [PR126961]
    
    Running the pr104116 tests with SVE2 which implements IFN_DIV_POW2 results in
    
    FAIL: gcc.dg/vect/pr104116-ceil-div-2.c execution test
    FAIL: gcc.dg/vect/pr104116-ceil-div-pow2.c execution test
    FAIL: gcc.dg/vect/pr104116-ceil-mod-2.c execution test
    FAIL: gcc.dg/vect/pr104116-ceil-mod-pow2.c execution test
    FAIL: gcc.dg/vect/pr104116-ceil-udiv-2.c execution test
    FAIL: gcc.dg/vect/pr104116-ceil-udiv-pow2.c execution test
    FAIL: gcc.dg/vect/pr104116-ceil-umod-2.c execution test
    FAIL: gcc.dg/vect/pr104116-ceil-umod-pow2.c execution test
    FAIL: gcc.dg/vect/pr104116-floor-div-2.c execution test
    FAIL: gcc.dg/vect/pr104116-floor-div-pow2.c execution test
    FAIL: gcc.dg/vect/pr104116-floor-mod-2.c execution test
    FAIL: gcc.dg/vect/pr104116-floor-mod-pow2.c execution test
    FAIL: gcc.dg/vect/pr104116-round-div-2.c execution test
    FAIL: gcc.dg/vect/pr104116-round-div-pow2.c execution test
    FAIL: gcc.dg/vect/pr104116-round-mod-2.c execution test
    FAIL: gcc.dg/vect/pr104116-round-mod-pow2.c execution test
    FAIL: gcc.dg/vect/pr104116-round-udiv-2.c execution test
    FAIL: gcc.dg/vect/pr104116-round-udiv-pow2.c execution test
    FAIL: gcc.dg/vect/pr104116-round-umod-2.c execution test
    FAIL: gcc.dg/vect/pr104116-round-umod-pow2.c execution test
    
    The first part is that add_code_for_floorceilround_divmod expects that the 6th
    parameter be the remainder.  This is passed correctly for most uses except for
    one where instead the shifted quotient is passed instead which causes a
    miscompile.
    
    Secondly IFN_DIV_POW2 is defined for only signed types.
    
    DEF_INTERNAL_OPTAB_FN (DIV_POW2, ECF_CONST | ECF_NOTHROW, sdiv_pow2, binary)
    
    and the documentation says
    
    @itemx @samp{sdiv_pow2@var{m}3}
    Signed division by power-of-2 immediate. Equivalent to:
    
    However the code does not actually check that the type is signed.
    So we end up using the IFN for unsigned division as well resulting in the
    failures for the unsigned testcases.
    
    gcc/ChangeLog:
    
            PR tree-optimization/126961
            * tree-vect-patterns.cc (vect_recog_divmod_pattern): Fix remainder use
            and add signedness check.

Diff:
---
 gcc/tree-vect-patterns.cc | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
index fd1232cc7552..ef128d75e109 100644
--- a/gcc/tree-vect-patterns.cc
+++ b/gcc/tree-vect-patterns.cc
@@ -5274,7 +5274,8 @@ vect_recog_divmod_pattern (vec_info *vinfo,
 
       /* Check if the target supports this internal function.  */
       internal_fn ifn = IFN_DIV_POW2;
-      if (direct_internal_fn_supported_p (ifn, vectype, OPTIMIZE_FOR_SPEED))
+      if (!TYPE_UNSIGNED (itype)
+	  && direct_internal_fn_supported_p (ifn, vectype, OPTIMIZE_FOR_SPEED))
 	{
 	  tree shift = build_int_cst (itype, tree_log2 (oprnd1));
 
@@ -5288,16 +5289,15 @@ vect_recog_divmod_pattern (vec_info *vinfo,
 	      def_stmt
 		= gimple_build_assign (t1, LSHIFT_EXPR, var_div, shift);
 	      append_pattern_def_seq (vinfo, stmt_vinfo, def_stmt);
-	      pattern_stmt
-		= gimple_build_assign (vect_recog_temp_ssa_var (itype, NULL),
-				       MINUS_EXPR, oprnd0, t1);
+	      tree r = vect_recog_temp_ssa_var (itype, NULL);
+	      pattern_stmt = gimple_build_assign (r, MINUS_EXPR, oprnd0, t1);
 	      if (is_flclrd_moddiv_p)
 		{
 		  append_pattern_def_seq (vinfo, stmt_vinfo, pattern_stmt);
 		  pattern_stmt
 		    = add_code_for_floorceilround_divmod (vectype, vinfo,
 							  stmt_vinfo, rhs_code,
-							  var_div, t1, oprnd0,
+							  var_div, r, oprnd0,
 							  oprnd1, itype);
 		  if (pattern_stmt == NULL)
 		    return NULL;