Handle a null lhs in expand_direct_optab_fn (PR85862)

[Richard Sandiford]

This PR showed that the normal function for expanding directly-mapped
internal functions didn't handle the case in which the call was only
being kept for its side-effects.

Tested on aarch64-linux-gnu (with and without SVE), aarch64_be-elf
and x86_64-linux-gnu.  OK to install?

Richard


2018-05-22  Richard Sandiford  <richard.sandif...@linaro.org>

gcc/
        PR middle-end/85862
        * internal-fn.c (expand_direct_optab_fn): Cope with a null lhs.

gcc/testsuite/
        PR middle-end/85862
        * gcc.dg/torture/pr85862.c: New test.

Index: gcc/internal-fn.c
===================================================================
--- gcc/internal-fn.c   2018-05-18 09:26:37.734714355 +0100
+++ gcc/internal-fn.c   2018-05-22 07:56:26.130013854 +0100
@@ -2891,14 +2891,15 @@ expand_direct_optab_fn (internal_fn fn,
   insn_code icode = direct_optab_handler (optab, TYPE_MODE (types.first));
 
   tree lhs = gimple_call_lhs (stmt);
-  tree lhs_type = TREE_TYPE (lhs);
-  rtx lhs_rtx = expand_expr (lhs, NULL_RTX, VOIDmode, EXPAND_WRITE);
+  rtx lhs_rtx = NULL_RTX;
+  if (lhs)
+    lhs_rtx = expand_expr (lhs, NULL_RTX, VOIDmode, EXPAND_WRITE);
 
   /* Do not assign directly to a promoted subreg, since there is no
      guarantee that the instruction will leave the upper bits of the
      register in the state required by SUBREG_PROMOTED_SIGN.  */
   rtx dest = lhs_rtx;
-  if (GET_CODE (dest) == SUBREG && SUBREG_PROMOTED_VAR_P (dest))
+  if (dest && GET_CODE (dest) == SUBREG && SUBREG_PROMOTED_VAR_P (dest))
     dest = NULL_RTX;
 
   create_output_operand (&ops[0], dest, insn_data[icode].operand[0].mode);
@@ -2917,7 +2918,7 @@ expand_direct_optab_fn (internal_fn fn,
     }
 
   expand_insn (icode, nargs + 1, ops);
-  if (!rtx_equal_p (lhs_rtx, ops[0].value))
+  if (lhs_rtx && !rtx_equal_p (lhs_rtx, ops[0].value))
     {
       /* If the return value has an integral type, convert the instruction
         result to that type.  This is useful for things that return an
@@ -2931,7 +2932,7 @@ expand_direct_optab_fn (internal_fn fn,
          /* If this is a scalar in a register that is stored in a wider
             mode than the declared mode, compute the result into its
             declared mode and then convert to the wider mode.  */
-         gcc_checking_assert (INTEGRAL_TYPE_P (lhs_type));
+         gcc_checking_assert (INTEGRAL_TYPE_P (TREE_TYPE (lhs)));
          rtx tmp = convert_to_mode (GET_MODE (lhs_rtx), ops[0].value, 0);
          convert_move (SUBREG_REG (lhs_rtx), tmp,
                        SUBREG_PROMOTED_SIGN (lhs_rtx));
@@ -2940,7 +2941,7 @@ expand_direct_optab_fn (internal_fn fn,
        emit_move_insn (lhs_rtx, ops[0].value);
       else
        {
-         gcc_checking_assert (INTEGRAL_TYPE_P (lhs_type));
+         gcc_checking_assert (INTEGRAL_TYPE_P (TREE_TYPE (lhs)));
          convert_move (lhs_rtx, ops[0].value, 0);
        }
     }
Index: gcc/testsuite/gcc.dg/torture/pr85862.c
===================================================================
--- /dev/null   2018-04-20 16:19:46.369131350 +0100
+++ gcc/testsuite/gcc.dg/torture/pr85862.c      2018-05-22 07:56:26.131013803 
+0100
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-fexceptions -fnon-call-exceptions" } */
+/* { dg-additional-options "-fexceptions -fnon-call-exceptions -mfma" { target 
i?86-*-* x86_64-*-* } } */
+
+void
+ki (double nq)
+{
+  double no = 1.1 * nq - nq;
+}