rs6000: Don't add an immediate to r0 (PR80966)

If there is a large stack frame the rs6000 -fstack-limit code would
calculate the new stack pointer value using two insns (an addis and
an addi), with r0 as temporary.  Such instructions do not exist.

This patch changes add<mode>3 to expand using a different strategy in
such cases; to FAIL if there is no way to do it (namely, if the source
is r0 and there is no way to get a temporary reg); and it changes
rs6000_emit_allocate_stack to assert gen_add3_insn did in fact emit
instructions.


	PR target/80966
	* config/rs6000/rs6000.c (rs6000_emit_allocate_stack): Assert that
	gen_add3_insn did not fail.
	* config/rs6000/rs6000.md (add<mode>3): If asked to add a constant to
	r0, construct that number in a temporary reg and add that reg to r0.
	If asked to put the result in r0 as well, fail.

gcc/testsuite/
	* gcc.target/powerpc/stack-limit.c: New testcase.

From-SVN: r249046

gcc/ChangeLog

+2017-06-09  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	PR target/80966
+	* config/rs6000/rs6000.c (rs6000_emit_allocate_stack): Assert that
+	gen_add3_insn did not fail.
+	* config/rs6000/rs6000.md (add<mode>3): If asked to add a constant to
+	r0, construct that number in a temporary reg and add that reg to r0.
+	If asked to put the result in r0 as well, fail.
+
 2017-06-08  Will Schmidt  <will_schmidt@vnet.ibm.com>
 
 	* config/rs6000/rs6000.c (rs6000_gimple_fold_builtin): Add handling

gcc/config/rs6000/rs6000.c

@@ -27005,9 +27005,11 @@ rs6000_emit_allocate_stack (HOST_WIDE_INT size, rtx copy_reg, int copy_off)
 	  && REGNO (stack_limit_rtx) > 1
 	  && REGNO (stack_limit_rtx) <= 31)
 	{
-	  emit_insn (gen_add3_insn (tmp_reg, stack_limit_rtx, GEN_INT (size)));
-	  emit_insn (gen_cond_trap (LTU, stack_reg, tmp_reg,
-				    const0_rtx));
+	  rtx_insn *insn
+	    = gen_add3_insn (tmp_reg, stack_limit_rtx, GEN_INT (size));
+	  gcc_assert (insn);
+	  emit_insn (insn);
+	  emit_insn (gen_cond_trap (LTU, stack_reg, tmp_reg, const0_rtx));
 	}
       else if (GET_CODE (stack_limit_rtx) == SYMBOL_REF
 	       && TARGET_32BIT

gcc/config/rs6000/rs6000.md

@@ -1629,6 +1629,17 @@
 		  || rtx_equal_p (operands[0], operands[1]))
 		 ? operands[0] : gen_reg_rtx (<MODE>mode));
 
+      /* Adding a constant to r0 is not a valid insn, so use a different
+	 strategy in that case.  */
+      if (REGNO (operands[1]) == 0 || REGNO (tmp) == 0)
+	{
+	  if (operands[0] == operands[1])
+	    FAIL;
+	  rs6000_emit_move (operands[0], operands[2], <MODE>mode);
+	  emit_insn (gen_add<mode>3 (operands[0], operands[1], operands[0]));
+	  DONE;
+	}
+
       HOST_WIDE_INT val = INTVAL (operands[2]);
       HOST_WIDE_INT low = ((val & 0xffff) ^ 0x8000) - 0x8000;
       HOST_WIDE_INT rest = trunc_int_for_mode (val - low, <MODE>mode);

gcc/testsuite/ChangeLog

+2017-06-09  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	PR target/80966
+	* gcc.target/powerpc/stack-limit.c: New testcase.
+
 2017-06-08  Will Schmidt  <will_schmidt@vnet.ibm.com>
 
 	* testsuite/gcc.target/powerpc/fold-vec-logical-eqv-char.c: New.

gcc/testsuite/gcc.target/powerpc/stack-limit.c

+/* { dg-options "-O0 -fstack-limit-register=r14" } */
+
+// PR80966
+
+int foo (int i)
+{
+  char arr[135000];
+
+  arr[i] = 0;
+}