Hi!

This patch is just a partial fix, combine.c has lots of other code that was
written before vector modes were introduced and won't work well with them.

The patch also uses ? x : const_true_rtx rather than
? CONSTM1_RTX (GET_MODE (x)) : const_true_rtx
or some new CONST_TRUE_RTX (GET_MODE (x)), so that it is backportable, that
can be changed on the trunk incrementally.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk and
release branches?

2018-08-27  Jakub Jelinek  <ja...@redhat.com>

        PR rtl-optimization/87065
        * combine.c (simplify_if_then_else): Formatting fix.
        (if_then_else_cond): Guard MULT optimization with SCALAR_INT_MODE_P
        check.
        (known_cond): Don't return const_true_rtx for vector modes.  Use
        CONST0_RTX instead of const0_rtx.  Formatting fixes.

        * gcc.target/i386/pr87065.c: New test.

--- gcc/combine.c.jj    2018-08-26 22:42:24.053753908 +0200
+++ gcc/combine.c       2018-08-27 08:58:26.867124011 +0200
@@ -6495,7 +6495,7 @@ simplify_if_then_else (rtx x)
                          pc_rtx, pc_rtx, 0, 0, 0);
       if (reg_mentioned_p (from, false_rtx))
        false_rtx = subst (known_cond (copy_rtx (false_rtx), false_code,
-                                  from, false_val),
+                                      from, false_val),
                           pc_rtx, pc_rtx, 0, 0, 0);
 
       SUBST (XEXP (x, 1), swapped ? false_rtx : true_rtx);
@@ -9335,6 +9335,7 @@ if_then_else_cond (rtx x, rtx *ptrue, rt
 
          if (COMPARISON_P (cond0)
              && COMPARISON_P (cond1)
+             && SCALAR_INT_MODE_P (mode)
              && ((GET_CODE (cond0) == reversed_comparison_code (cond1, NULL)
                   && rtx_equal_p (XEXP (cond0, 0), XEXP (cond1, 0))
                   && rtx_equal_p (XEXP (cond0, 1), XEXP (cond1, 1)))
@@ -9515,12 +9516,12 @@ known_cond (rtx x, enum rtx_code cond, r
          if (COMPARISON_P (x))
            {
              if (comparison_dominates_p (cond, code))
-               return const_true_rtx;
+               return VECTOR_MODE_P (GET_MODE (x)) ? x : const_true_rtx;
 
              code = reversed_comparison_code (x, NULL);
              if (code != UNKNOWN
                  && comparison_dominates_p (cond, code))
-               return const0_rtx;
+               return CONST0_RTX (GET_MODE (x));
              else
                return x;
            }
@@ -9563,7 +9564,7 @@ known_cond (rtx x, enum rtx_code cond, r
          /* We must simplify subreg here, before we lose track of the
             original inner_mode.  */
          new_rtx = simplify_subreg (GET_MODE (x), r,
-                                inner_mode, SUBREG_BYTE (x));
+                                    inner_mode, SUBREG_BYTE (x));
          if (new_rtx)
            return new_rtx;
          else
@@ -9588,7 +9589,7 @@ known_cond (rtx x, enum rtx_code cond, r
          /* We must simplify the zero_extend here, before we lose
             track of the original inner_mode.  */
          new_rtx = simplify_unary_operation (ZERO_EXTEND, GET_MODE (x),
-                                         r, inner_mode);
+                                             r, inner_mode);
          if (new_rtx)
            return new_rtx;
          else
--- gcc/testsuite/gcc.target/i386/pr87065.c.jj  2018-08-27 08:46:16.302406144 
+0200
+++ gcc/testsuite/gcc.target/i386/pr87065.c     2018-08-27 08:50:37.179025375 
+0200
@@ -0,0 +1,22 @@
+/* PR rtl-optimization/87065 */
+/* { dg-do compile } */
+/* { dg-options "-O3 -mxop -mprefer-vector-width=128" } */
+
+int a, c, d, e;
+short *b;
+
+void
+foo (void)
+{
+  short *g = b;
+  int h = 1;
+  unsigned i;
+  for (; h <= 1; h++)
+    g = (short *) &c;
+  for (; c; c++)
+    {
+      for (; i <= 1; i++)
+       ;
+      a ^= (a > 0 <= i) + ((e += d) == 0 ?: (*g = 8));
+    }
+}

        Jakub

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