rs6000: Fix stack clash for big residuals (PR85287)

The stack clash protection code had a logic error in how it decided
whether to put the final update size in a register, or to emit it
directly in an insn.  This fixes it.  It also tidies some surrounding
code.


	PR target/85287
	* gcc/config/rs6000/rs6000.md (allocate_stack): Put the residual size
	for stack clash protection in a register whenever we need it to be in
	a register.

From-SVN: r259299

gcc/ChangeLog

 2018-04-10  Segher Boessenkool  <segher@kernel.crashing.org>
 
+	* gcc/config/rs6000/rs6000.md (allocate_stack): Put the residual size
+	for stack clash protection in a register whenever we need it to be in
+	a register.
+
+2018-04-10  Segher Boessenkool  <segher@kernel.crashing.org>
+
 	* common/config/rs6000/rs6000-common.c (rs6000_option_init_struct):
 	Enable -fasynchronous-unwind-tables by default if OBJECT_FORMAT_ELF.
 

gcc/config/rs6000/rs6000.md

@@ -9783,14 +9783,12 @@
       /* Now handle residuals.  We just have to set operands[1] correctly
 	 and let the rest of the expander run.  */
       operands[1] = residual;
-      if (!CONST_INT_P (residual))
-	operands[1] = force_reg (Pmode, operands[1]);
     }
 
-  if (GET_CODE (operands[1]) != CONST_INT
-      || INTVAL (operands[1]) < -32767
-      || INTVAL (operands[1]) > 32768)
+  if (!(CONST_INT_P (operands[1])
+	&& IN_RANGE (INTVAL (operands[1]), -32767, 32768)))
     {
+      operands[1] = force_reg (Pmode, operands[1]);
       neg_op0 = gen_reg_rtx (Pmode);
       if (TARGET_32BIT)
 	emit_insn (gen_negsi2 (neg_op0, operands[1]));
@@ -9798,7 +9796,7 @@
 	emit_insn (gen_negdi2 (neg_op0, operands[1]));
     }
   else
-    neg_op0 = GEN_INT (- INTVAL (operands[1]));
+    neg_op0 = GEN_INT (-INTVAL (operands[1]));
 
   insn = emit_insn ((* ((TARGET_32BIT) ? gen_movsi_update_stack
 				       : gen_movdi_di_update_stack))