c++: Fix up constant expression __builtin_convertvector folding [PR104472]

The following testcase ICEs, because due to the -frounding-math
fold_const_call fails, which is it returns NULL, and returning NULL from
cxx_eval* is wrong, all the callers rely on them to either return folded
value or original with *non_constant_p = true.

The following patch does that, and additionally falls through into the
default case where there is diagnostics for the !ctx->quiet case too.

2022-02-11  Jakub Jelinek  <jakub@redhat.com>

	PR c++/104472
	* constexpr.cc (cxx_eval_internal_function) <case IFN_VEC_CONVERT>:
	Only return fold_const_call result if it is non-NULL.  Otherwise
	fall through into the default: case to return t, set *non_constant_p
	and emit diagnostics if needed.

	* g++.dg/cpp0x/constexpr-104472.C: New test.

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 9b8e0ec..87f3a7b 100644 (file)
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -1840,13 +1840,10 @@ cxx_eval_internal_function (const constexpr_ctx *ctx, tree t,
                                                 false, non_constant_p,
                                                 overflow_p);
        if (TREE_CODE (arg) == VECTOR_CST)
-         return fold_const_call (CFN_VEC_CONVERT, TREE_TYPE (t), arg);
-       else
-         {
-           *non_constant_p = true;
-           return t;
-         }
+         if (tree r = fold_const_call (CFN_VEC_CONVERT, TREE_TYPE (t), arg))
+           return r;
       }
+      /* FALLTHRU */
 
     default:
       if (!ctx->quiet)

diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-104472.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-104472.C
new file mode 100644 (file)
index 0000000..c9c8bf4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-104472.C
@@ -0,0 +1,9 @@
+// PR c++/104472
+// { dg-options "-O2 -frounding-math" }
+// { dg-add-options float16 }
+// { dg-require-effective-target float16 }
+
+typedef short __attribute__((__vector_size__ (16))) V;
+typedef _Float16 __attribute__((__vector_size__ (16))) F;
+
+V v = __builtin_convertvector (__builtin_convertvector ((V){5534}, F), V) < 8;