cse: Workaround GCC < 5 bug in cse_insn [PR111852]

Before the r5-3834 commit for PR63362, GCC 4.8-4.9 refuses to compile
cse.cc which contains a variable with rtx_def type, because rtx_def
contains a union with poly_uint16 element.  poly_int template has
defaulted default constructor and a variadic template constructor which
could have empty parameter pack. GCC < 5 treated it as non-trivially
constructible class and deleted rtunion and rtx_def default constructors.

For the cse_insn purposes, all we need is a variable with size and alignment
of rtx_def, not necessarily rtx_def itself, which we then memset to 0 and
fill in like rtx is normally allocated from heap, so this patch for
GCC_VERSION < 5000 uses an unsigned char array of the right size/alignment.

2023-10-18  Jakub Jelinek  <jakub@redhat.com>

	PR bootstrap/111852
	* cse.cc (cse_insn): Add workaround for GCC 4.8-4.9, instead of
	using rtx_def type for memory_extend_buf, use unsigned char
	arrayy with size of rtx_def and its alignment.

diff --git a/gcc/cse.cc b/gcc/cse.cc
index c46870059e6c4069f60c4351918da244abb14071..f9603fdfd4373385939e8153a849d6b3d37c9186 100644 (file)
--- a/gcc/cse.cc
+++ b/gcc/cse.cc
@@ -4951,8 +4951,15 @@ cse_insn (rtx_insn *insn)
          && is_a <scalar_int_mode> (mode, &int_mode)
          && (extend_op = load_extend_op (int_mode)) != UNKNOWN)
        {
+#if GCC_VERSION >= 5000
          struct rtx_def memory_extend_buf;
          rtx memory_extend_rtx = &memory_extend_buf;
+#else
+         /* Workaround GCC < 5 bug, fixed in r5-3834 as part of PR63362
+            fix.  */
+         alignas (rtx_def) unsigned char memory_extended_buf[sizeof (rtx_def)];
+         rtx memory_extend_rtx = (rtx) &memory_extended_buf[0];
+#endif
 
          /* Set what we are trying to extend and the operation it might
             have been extended with.  */