Tighten check for vector types in fold_convertible_p (PR 92741)

[Richard Sandiford]

In this PR, IPA-CP was misled into using NOP_EXPR rather than
VIEW_CONVERT_EXPR to reinterpret a vector of 4 shorts as a vector
of 2 ints.  This tripped the tree-cfg.c assert I'd added in r278245.

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

Richard


2019-12-02  Richard Sandiford  <richard.sandif...@arm.com>

gcc/
        PR middle-end/92741
        * fold-const.c (fold_convertible_p): Check vector types more
        thoroughly.

gcc/testsuite/
        PR middle-end/92741
        * gcc.dg/pr92741.c: New test.

Index: gcc/fold-const.c
===================================================================
--- gcc/fold-const.c    2019-11-18 15:27:36.053367794 +0000
+++ gcc/fold-const.c    2019-12-02 16:25:02.662405351 +0000
@@ -2375,10 +2375,15 @@ fold_convertible_p (const_tree type, con
 
     case REAL_TYPE:
     case FIXED_POINT_TYPE:
-    case VECTOR_TYPE:
     case VOID_TYPE:
       return TREE_CODE (type) == TREE_CODE (orig);
 
+    case VECTOR_TYPE:
+      return (VECTOR_TYPE_P (orig)
+             && known_eq (TYPE_VECTOR_SUBPARTS (type),
+                          TYPE_VECTOR_SUBPARTS (orig))
+             && fold_convertible_p (TREE_TYPE (type), TREE_TYPE (orig)));
+
     default:
       return false;
     }
Index: gcc/testsuite/gcc.dg/pr92741.c
===================================================================
--- /dev/null   2019-09-17 11:41:18.176664108 +0100
+++ gcc/testsuite/gcc.dg/pr92741.c      2019-12-02 16:25:02.662405351 +0000
@@ -0,0 +1,19 @@
+/* { dg-options "-O2 -fexceptions -fnon-call-exceptions -fno-inline" } */
+
+typedef int vh __attribute__ ((__vector_size__ (2 * sizeof (int))));
+typedef short int cq __attribute__ ((__vector_size__ (4 * sizeof (short 
int))));
+
+static void
+id (int *r8, vh *tu)
+{
+  *(vh *) r8 = *tu;
+}
+
+void
+mr (void)
+{
+  int r8;
+  cq he = { 0, };
+
+  id (&r8, (vh *) &he);
+}