Fix recent bug in canonicalize_comparison (PR87026)

The new code testing which way a comparison is best expressed creates
a pseudoregister (by hand) and creates some insns with that.  Such
insns will no longer recog() when pseudo-registers are no longer
aloowed (after reload).  But we have an ifcvt pass after reload (ce3).

This patch simply returns if we cannot create pseudos.


	PR rtl-optimization/87026
	* expmed.c (canonicalize_comparison): If we can no longer create
	pseudoregisters, don't.

From-SVN: r263810

gcc/ChangeLog

+2018-08-23  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	PR rtl-optimization/87026
+	* expmed.c (canonicalize_comparison): If we can no longer create
+	pseudoregisters, don't.
+
 2018-08-23  Richard Earnshaw  <rearnsha@arm.com>
 
 	PR target/86951

gcc/expmed.c

@@ -6243,6 +6243,10 @@ canonicalize_comparison (machine_mode mode, enum rtx_code *code, rtx *imm)
   if (overflow)
     return;
 
+  /* The following creates a pseudo; if we cannot do that, bail out.  */
+  if (!can_create_pseudo_p ())
+    return;
+
   rtx reg = gen_rtx_REG (mode, LAST_VIRTUAL_REGISTER + 1);
   rtx new_imm = immed_wide_int_const (imm_modif, mode);