[PATCH] expr: Fix up VEC_PACK_TRUNC_EXPR expansion [PR101046]

[Jakub Jelinek via Gcc-patches]

Hi!

The following testcase ICEs, because we have a mode mismatch.
VEC_PACK_TRUNC_EXPR's operands have different modes from the result
(same vector mode size but twice as large element),
but we were passing non-NULL subtarget with the mode of the result
to the expansion of its arguments, so the VEC_PERM_EXPR in one of the
operands which had V8SImode operands and result had V16HImode target.

Fixed by clearing the subtarget if we are changing mode.

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

2021-06-15  Jakub Jelinek  <ja...@redhat.com>

        PR target/101046
        * expr.c (expand_expr_real_2) <case VEC_PACK_FIX_TRUNC_EXPR,
        case VEC_PACK_TRUNC_EXPR>: Clear subtarget when changing mode.

        * gcc.target/i386/pr101046.c: New test.

--- gcc/expr.c.jj       2021-05-21 21:09:08.000000000 +0200
+++ gcc/expr.c  2021-06-14 11:02:28.821342367 +0200
@@ -9998,6 +9998,7 @@ expand_expr_real_2 (sepops ops, rtx targ
     case VEC_PACK_SAT_EXPR:
     case VEC_PACK_FIX_TRUNC_EXPR:
       mode = TYPE_MODE (TREE_TYPE (treeop0));
+      subtarget = NULL_RTX;
       goto binop;
 
     case VEC_PACK_TRUNC_EXPR:
@@ -10021,6 +10022,7 @@ expand_expr_real_2 (sepops ops, rtx targ
          return eops[0].value;
        }
       mode = TYPE_MODE (TREE_TYPE (treeop0));
+      subtarget = NULL_RTX;
       goto binop;
 
     case VEC_PACK_FLOAT_EXPR:
--- gcc/testsuite/gcc.target/i386/pr101046.c.jj 2021-06-14 11:10:18.661701929 
+0200
+++ gcc/testsuite/gcc.target/i386/pr101046.c    2021-06-14 11:09:26.439439991 
+0200
@@ -0,0 +1,15 @@
+/* PR target/101046 */
+/* { dg-do compile } */
+/* { dg-options "-ftree-ter -mavx512bw -mavx512vl" } */
+
+typedef unsigned short __attribute__((__vector_size__(16))) U;
+typedef unsigned int __attribute__((__vector_size__(16))) V;
+typedef unsigned int __attribute__((__vector_size__(32))) W;
+
+U
+foo (void)
+{
+  return __builtin_convertvector (__builtin_shufflevector ((V){}, (W){},
+                                                          0, 0, 1, 0,
+                                                          5, 5, 0, 2), U);
+}

        Jakub