[PATCH v2] Return a NULL rtx when targets don't support cbranchcc4 or predicate check fails in prepare_cmp_insn

[HAO CHEN GUI <guihaoc@linux.ibm.com>]

Hi,
  It gets an assertion failure when targers don't support cbranchcc4 or
predicate check fails in prepare_cmp_insn. prepare_cmp_insn is a help
function to generate compare rtx, so it should not assume that cbranchcc4
is existing or all sub-CC modes are supported on one target. I think it
should return the NULL rtx when cbranchcc4 is not supported or predicate check
fails, as its callers already check if the return value is null or not for CC
mode. This patch just does the change.

  Bootstrapped and tested on powerpc64-linux BE/LE and x86 with no regressions.
Is this okay for trunk? Any recommendations? Thanks a lot.


ChangeLog
2022-12-05  Haochen Gui <guihaoc@linux.ibm.com>

gcc/
	* optabs.cc (prepare_cmp_insn): Return a NULL rtx other than assertion
	failure when targets don't have cbranch optab or predicate check
	fails.

patch.diff
diff --git a/gcc/optabs.cc b/gcc/optabs.cc
index 165f8d1fa22..f6d3242479b 100644
--- a/gcc/optabs.cc
+++ b/gcc/optabs.cc
@@ -4484,10 +4484,14 @@ prepare_cmp_insn (rtx x, rtx y, enum rtx_code comparison, rtx size,
     {
       enum insn_code icode = optab_handler (cbranch_optab, CCmode);
       test = gen_rtx_fmt_ee (comparison, VOIDmode, x, y);
-      gcc_assert (icode != CODE_FOR_nothing
-                  && insn_operand_matches (icode, 0, test));
-      *ptest = test;
-      return;
+      if (icode != CODE_FOR_nothing
+	  && insn_operand_matches (icode, 0, test))
+	{
+	  *ptest = test;
+	  return;
+	}
+      else
+	goto fail;
     }

   mclass = GET_MODE_CLASS (mode);