[nvptx, PR83589] Workaround for branch-around-nothing JIT bug

2018-01-23  Tom de Vries  <tom@codesourcery.com>

	PR target/83589
	* config/nvptx/nvptx.c (WORKAROUND_PTXJIT_BUG_2): Define to 1.
	(nvptx_pc_set, nvptx_condjump_label): New function. Copy from jump.c.
	Add strict parameter.
	(prevent_branch_around_nothing): Insert dummy insn between branch to
	label and label with no ptx insn inbetween.
	* config/nvptx/nvptx.md (define_insn "fake_nop"): New insn.

	* testsuite/libgomp.oacc-c-c++-common/pr83589.c: New test.

---
 gcc/config/nvptx/nvptx.c                           | 92 ++++++++++++++++++++++
 gcc/config/nvptx/nvptx.md                          |  9 +++
 .../testsuite/libgomp.oacc-c-c++-common/pr83589.c  | 21 +++++
 3 files changed, 122 insertions(+)

diff --git a/gcc/config/nvptx/nvptx.c b/gcc/config/nvptx/nvptx.c
index 3516740..e55b426 100644
--- a/gcc/config/nvptx/nvptx.c
+++ b/gcc/config/nvptx/nvptx.c
@@ -78,6 +78,7 @@
 #include "target-def.h"
 
 #define WORKAROUND_PTXJIT_BUG 1
+#define WORKAROUND_PTXJIT_BUG_2 1
 
 /* The various PTX memory areas an object might reside in.  */
 enum nvptx_data_area
@@ -4363,6 +4364,93 @@ nvptx_neuter_pars (parallel *par, unsigned modes, unsigned outer)
     nvptx_neuter_pars (par->next, modes, outer);
 }
 
+#if WORKAROUND_PTXJIT_BUG_2
+/* Variant of pc_set that only requires JUMP_P (INSN) if STRICT.  This variant
+   is needed in the nvptx target because the branches generated for
+   parititioning are NONJUMP_INSN_P, not JUMP_P.  */
+
+static rtx
+nvptx_pc_set (const rtx_insn *insn, bool strict = true)
+{
+  rtx pat;
+  if ((strict && !JUMP_P (insn))
+      || (!strict && !INSN_P (insn)))
+    return NULL_RTX;
+  pat = PATTERN (insn);
+
+  /* The set is allowed to appear either as the insn pattern or
+     the first set in a PARALLEL.  */
+  if (GET_CODE (pat) == PARALLEL)
+    pat = XVECEXP (pat, 0, 0);
+  if (GET_CODE (pat) == SET && GET_CODE (SET_DEST (pat)) == PC)
+    return pat;
+
+  return NULL_RTX;
+}
+
+/* Variant of condjump_label that only requires JUMP_P (INSN) if STRICT.  */
+
+static rtx
+nvptx_condjump_label (const rtx_insn *insn, bool strict = true)
+{
+  rtx x = nvptx_pc_set (insn, strict);
+
+  if (!x)
+    return NULL_RTX;
+  x = SET_SRC (x);
+  if (GET_CODE (x) == LABEL_REF)
+    return x;
+  if (GET_CODE (x) != IF_THEN_ELSE)
+    return NULL_RTX;
+  if (XEXP (x, 2) == pc_rtx && GET_CODE (XEXP (x, 1)) == LABEL_REF)
+    return XEXP (x, 1);
+  if (XEXP (x, 1) == pc_rtx && GET_CODE (XEXP (x, 2)) == LABEL_REF)
+    return XEXP (x, 2);
+  return NULL_RTX;
+}
+
+/* Insert a dummy ptx insn when encountering a branch to a label with no ptx
+   insn inbetween the branch and the label.  This works around a JIT bug
+   observed at driver version 384.111, at -O0 for sm_50.  */
+
+static void
+prevent_branch_around_nothing (void)
+{
+  rtx_insn *seen_label = 0;
+    for (rtx_insn *insn = get_insns (); insn; insn = NEXT_INSN (insn))
+      {
+	if (seen_label == 0)
+	  {
+	    if (INSN_P (insn) && condjump_p (insn))
+	      seen_label = label_ref_label (nvptx_condjump_label (insn, false));
+
+	    continue;
+	  }
+
+	if (NOTE_P (insn))
+	  continue;
+
+	if (INSN_P (insn))
+	  switch (recog_memoized (insn))
+	    {
+	    case CODE_FOR_nvptx_fork:
+	    case CODE_FOR_nvptx_forked:
+	    case CODE_FOR_nvptx_joining:
+	    case CODE_FOR_nvptx_join:
+	      continue;
+	    default:
+	      seen_label = 0;
+	      continue;
+	    }
+
+	if (LABEL_P (insn) && insn == seen_label)
+	  emit_insn_before (gen_fake_nop (), insn);
+
+	seen_label = 0;
+      }
+  }
+#endif
+
 /* PTX-specific reorganization
    - Split blocks at fork and join instructions
    - Compute live registers
@@ -4442,6 +4530,10 @@ nvptx_reorg (void)
   if (TARGET_UNIFORM_SIMT)
     nvptx_reorg_uniform_simt ();
 
+#if WORKAROUND_PTXJIT_BUG_2
+  prevent_branch_around_nothing ();
+#endif
+
   regstat_free_n_sets_and_refs ();
 
   df_finish_pass (true);
diff --git a/gcc/config/nvptx/nvptx.md b/gcc/config/nvptx/nvptx.md
index 135479b..4f4453d 100644
--- a/gcc/config/nvptx/nvptx.md
+++ b/gcc/config/nvptx/nvptx.md
@@ -999,6 +999,15 @@
   ""
   "exit;")
 
+(define_insn "fake_nop"
+  [(const_int 2)]
+  ""
+  "{
+     .reg .u32 %%nop_src;
+     .reg .u32 %%nop_dst;
+     mov.u32 %%nop_dst, %%nop_src;
+   }")
+
 (define_insn "return"
   [(return)]
   ""
diff --git a/libgomp/testsuite/libgomp.oacc-c-c++-common/pr83589.c b/libgomp/testsuite/libgomp.oacc-c-c++-common/pr83589.c
new file mode 100644
index 0000000..a6ed5cf
--- /dev/null
+++ b/libgomp/testsuite/libgomp.oacc-c-c++-common/pr83589.c
@@ -0,0 +1,21 @@
+/* { dg-do run } */
+/* { dg-set-target-env-var GOMP_NVPTX_JIT "-O0" } */
+
+#define n 32
+
+int
+main (void)
+{
+  int arr_a[n];
+
+#pragma acc parallel copyout(arr_a) num_gangs(1) num_workers(1) vector_length(32)
+  {
+    #pragma acc loop vector
+    for (int m = 0; m < 32; m++)
+      ;
+
+    #pragma acc loop vector
+    for (int m = 0; m < 32; m++)
+      arr_a[m] = 0;
+  }
+}