AArch64 - disable CB[N]Z TB[N]Z when tracking speculation

The CB[N]Z and TB[N]Z instructions do not expose the comparison through
the condition code flags.  This makes it impossible to track speculative
execution through such a branch.  We can handle this relatively easily
by simply disabling the patterns in this case.

A side effect of this is that the split patterns for the atomic operations
need to also avoid generating these instructions.  They mostly have simple
fall-backs for this already.

	* config/aarch64/aarch64.md (cb<optab><mode>1): Disable when
	aarch64_track_speculation is true.
	(tb<optab><mode>1): Likewise.
	* config/aarch64/aarch64.c (aarch64_split_compare_regs): Do not
	generate CB[N]Z when tracking speculation.
	(aarch64_split_compare_and_swap): Likewise.
	(aarch64_split_atomic_op): Likewise.

(backported eaf891585b16ef84046ae73a01bb1c7189c682e9)

Change-Id: I0d0a090ef7bcf074b9e4d6ee115e71faa157962f
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@263172 138bc75d-0d04-0410-961f-82ee72b054a4

3 files changed, 43 insertions, 6 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 017782351db..384627cb3c1 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,15 @@
 2018-07-31  Richard Earnshaw  <rearnsha@arm.com>
 
+	* config/aarch64/aarch64.md (cb<optab><mode>1): Disable when
+	aarch64_track_speculation is true.
+	(tb<optab><mode>1): Likewise.
+	* config/aarch64/aarch64.c (aarch64_split_compare_regs): Do not
+	generate CB[N]Z when tracking speculation.
+	(aarch64_split_compare_and_swap): Likewise.
+	(aarch64_split_atomic_op): Likewise.
+
+2018-07-31  Richard Earnshaw  <rearnsha@arm.com>
+
 	* config/aarch64/aarch64.opt (mtrack-speculation): New target option.
 
 2018-07-31  Richard Earnshaw  <rearnsha@arm.com>
diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 795033faeae..975617f5f31 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -11650,7 +11650,16 @@ aarch64_split_compare_and_swap (rtx operands[])
 
   if (strong_zero_p)
     {
-      x = gen_rtx_NE (VOIDmode, rval, const0_rtx);
+      if (aarch64_track_speculation)
+	{
+	  /* Emit an explicit compare instruction, so that we can correctly
+	     track the condition codes.  */
+	  rtx cc_reg = aarch64_gen_compare_reg (NE, rval, const0_rtx);
+	  x = gen_rtx_NE (GET_MODE (cc_reg), cc_reg, const0_rtx);
+	}
+      else
+	x = gen_rtx_NE (VOIDmode, rval, const0_rtx);
+
       x = gen_rtx_IF_THEN_ELSE (VOIDmode, x,
 				gen_rtx_LABEL_REF (Pmode, label2), pc_rtx);
       aarch64_emit_unlikely_jump (gen_rtx_SET (pc_rtx, x));
@@ -11668,7 +11677,16 @@ aarch64_split_compare_and_swap (rtx operands[])
 
   if (!is_weak)
     {
-      x = gen_rtx_NE (VOIDmode, scratch, const0_rtx);
+      if (aarch64_track_speculation)
+	{
+	  /* Emit an explicit compare instruction, so that we can correctly
+	     track the condition codes.  */
+	  rtx cc_reg = aarch64_gen_compare_reg (NE, scratch, const0_rtx);
+	  x = gen_rtx_NE (GET_MODE (cc_reg), cc_reg, const0_rtx);
+	}
+      else
+	x = gen_rtx_NE (VOIDmode, scratch, const0_rtx);
+
       x = gen_rtx_IF_THEN_ELSE (VOIDmode, x,
 				gen_rtx_LABEL_REF (Pmode, label1), pc_rtx);
       aarch64_emit_unlikely_jump (gen_rtx_SET (pc_rtx, x));
@@ -12004,7 +12022,16 @@ aarch64_split_atomic_op (enum rtx_code code, rtx old_out, rtx new_out, rtx mem,
   aarch64_emit_store_exclusive (mode, cond, mem,
 				gen_lowpart (mode, new_out), model_rtx);
 
-  x = gen_rtx_NE (VOIDmode, cond, const0_rtx);
+  if (aarch64_track_speculation)
+    {
+      /* Emit an explicit compare instruction, so that we can correctly
+	 track the condition codes.  */
+      rtx cc_reg = aarch64_gen_compare_reg (NE, cond, const0_rtx);
+      x = gen_rtx_NE (GET_MODE (cc_reg), cc_reg, const0_rtx);
+    }
+  else
+    x = gen_rtx_NE (VOIDmode, cond, const0_rtx);
+
   x = gen_rtx_IF_THEN_ELSE (VOIDmode, x,
 			    gen_rtx_LABEL_REF (Pmode, label), pc_rtx);
   aarch64_emit_unlikely_jump (gen_rtx_SET (pc_rtx, x));
diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
index 6a03262cc06..bc8d736f595 100644
--- a/gcc/config/aarch64/aarch64.md
+++ b/gcc/config/aarch64/aarch64.md
@@ -597,7 +597,7 @@
 				(const_int 0))
 			   (label_ref (match_operand 1 "" ""))
 			   (pc)))]
-  ""
+  "!aarch64_track_speculation"
   {
     if (get_attr_length (insn) == 8)
       return aarch64_gen_far_branch (operands, 1, "Lcb", "<inv_cb>\\t%<w>0, ");
@@ -627,7 +627,7 @@
 	     (label_ref (match_operand 2 "" ""))
 	     (pc)))
    (clobber (reg:CC CC_REGNUM))]
-  ""
+  "!aarch64_track_speculation"
   {
     if (get_attr_length (insn) == 8)
       {
@@ -663,7 +663,7 @@
 			   (label_ref (match_operand 1 "" ""))
 			   (pc)))
    (clobber (reg:CC CC_REGNUM))]
-  ""
+  "!aarch64_track_speculation"
   {
     if (get_attr_length (insn) == 8)
       {