[PATCH] optabs: Don't use scalar conversions for vectors [PR93843]

[Richard Sandiford]

In this PR we had a conversion between two integer vectors that
both had scalar integer modes.  We then tried to implement the
conversion using the scalar optab for those modes, instead of
doing the conversion elementwise.

I wondered about letting through scalar modes for single-element
vectors, but I don't have any evidence that that's useful/necessary,
so it seemed better to keep things simple.

Tested on aarch64-linux-gnu, armeb-eabi and x86_64-linux-gnu.
OK to install?

Richard


2020-02-26  Richard Sandiford  <richard.sandif...@arm.com>

gcc/
        PR middle-end/93843
        * optabs-tree.c (supportable_convert_operation): Reject types with
        scalar modes.

gcc/testsuite/
        PR middle-end/93843
        * gcc.dg/vect/pr93843-1.c: New test.
        * gcc.dg/vect/pr93843-2.c: Likewise.
---
 gcc/optabs-tree.c                     |  5 +++++
 gcc/testsuite/gcc.dg/vect/pr93843-1.c | 21 +++++++++++++++++++++
 gcc/testsuite/gcc.dg/vect/pr93843-2.c | 11 +++++++++++
 3 files changed, 37 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/vect/pr93843-1.c
 create mode 100644 gcc/testsuite/gcc.dg/vect/pr93843-2.c

diff --git a/gcc/optabs-tree.c b/gcc/optabs-tree.c
index 3d829c27826..badd30bfda8 100644
--- a/gcc/optabs-tree.c
+++ b/gcc/optabs-tree.c
@@ -284,9 +284,14 @@ supportable_convert_operation (enum tree_code code,
   machine_mode m1,m2;
   bool truncp;
 
+  gcc_assert (VECTOR_TYPE_P (vectype_out) && VECTOR_TYPE_P (vectype_in));
+
   m1 = TYPE_MODE (vectype_out);
   m2 = TYPE_MODE (vectype_in);
 
+  if (!VECTOR_MODE_P (m1) || !VECTOR_MODE_P (m2))
+    return false;
+
   /* First check if we can done conversion directly.  */
   if ((code == FIX_TRUNC_EXPR
        && can_fix_p (m1,m2,TYPE_UNSIGNED (vectype_out), &truncp)
diff --git a/gcc/testsuite/gcc.dg/vect/pr93843-1.c 
b/gcc/testsuite/gcc.dg/vect/pr93843-1.c
new file mode 100644
index 00000000000..23a79ca4c96
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr93843-1.c
@@ -0,0 +1,21 @@
+char a;
+struct S { short b, c; } d;
+
+__attribute__((noipa)) void
+foo (int x)
+{
+  if (x != 4)
+    __builtin_abort ();
+}
+
+int
+main ()
+{
+  short *g = &d.c, *h = &d.b;
+  char e = 4 - a;
+  int f;
+  *h = *g = e;
+  for (f = 0; f < 2; f++)
+    foo (d.c);
+  return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/vect/pr93843-2.c 
b/gcc/testsuite/gcc.dg/vect/pr93843-2.c
new file mode 100644
index 00000000000..5fae3e5be17
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr93843-2.c
@@ -0,0 +1,11 @@
+char in[2] = {2, 2};
+short out[2] = {};
+
+int
+main()
+{
+  for (int i = 0; i < 2; ++i)
+    out[i] = in[i];
+  asm("":::"memory");
+  if (out[0] != 2) __builtin_abort();
+}