aarch64: Fix -mtrack-speculation for irreversible conditions [PR93341]

We can't yet represent the inverse of all conditions in rtl
(see g:865257c447cc50f5819e), triggering an ICE in the pass
that handles -mtrack-speculation.  Since we don't expect these
insns to be optimised in any way, the easiest fix seemed to be
to add an insn that reverses the condition internally.

2020-01-23  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	PR target/93341
	* config/aarch64/aarch64.md (UNSPEC_SPECULATION_TRACKER_REV): New
	unspec.
	(speculation_tracker_rev): New pattern.
	* config/aarch64/aarch64-speculation.cc (aarch64_do_track_speculation):
	Use speculation_tracker_rev to track the inverse condition.

gcc/testsuite/
	PR target/93341
	* gcc.target/aarch64/pr93341.c: New test.

gcc/ChangeLog

@@ -1,3 +1,12 @@
+2020-01-23  Richard Sandiford  <richard.sandiford@arm.com>
+
+	PR target/93341
+	* config/aarch64/aarch64.md (UNSPEC_SPECULATION_TRACKER_REV): New
+	unspec.
+	(speculation_tracker_rev): New pattern.
+	* config/aarch64/aarch64-speculation.cc (aarch64_do_track_speculation):
+	Use speculation_tracker_rev to track the inverse condition.
+
 2020-01-23  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/93381

gcc/config/aarch64/aarch64-speculation.cc

@@ -215,20 +215,13 @@ aarch64_do_track_speculation ()
 			  && REG_P (XEXP (cond, 0))
 			  && REGNO (XEXP (cond, 0)) == CC_REGNUM
 			  && XEXP (cond, 1) == const0_rtx);
-	      enum rtx_code inv_cond_code
+	      rtx branch_tracker = gen_speculation_tracker (copy_rtx (cond));
-		= reversed_comparison_code (cond, insn);
+	      rtx fallthru_tracker = gen_speculation_tracker_rev (cond);
-	      /* We should be able to reverse all conditions.  */
-	      gcc_assert (inv_cond_code != UNKNOWN);
-	      rtx inv_cond = gen_rtx_fmt_ee (inv_cond_code, GET_MODE (cond),
-					     copy_rtx (XEXP (cond, 0)),
-					     copy_rtx (XEXP (cond, 1)));
 	      if (inverted)
-		std::swap (cond, inv_cond);
+		std::swap (branch_tracker, fallthru_tracker);
 
-	      insert_insn_on_edge (gen_speculation_tracker (cond),
+	      insert_insn_on_edge (branch_tracker, BRANCH_EDGE (bb));
-				   BRANCH_EDGE (bb));
+	      insert_insn_on_edge (fallthru_tracker, FALLTHRU_EDGE (bb));
-	      insert_insn_on_edge (gen_speculation_tracker (inv_cond),
-				   FALLTHRU_EDGE (bb));
 	      needs_tracking = true;
 	    }
 	  else if (GET_CODE (PATTERN (insn)) == RETURN)

gcc/config/aarch64/aarch64.md

@@ -262,6 +262,7 @@
     UNSPEC_REV_SUBREG
     UNSPEC_REINTERPRET
     UNSPEC_SPECULATION_TRACKER
+    UNSPEC_SPECULATION_TRACKER_REV
     UNSPEC_COPYSIGN
     UNSPEC_TTEST		; Represent transaction test.
     UNSPEC_UPDATE_FFR
@@ -7219,6 +7220,20 @@
   [(set_attr "type" "csel")]
 )
 
+;; Like speculation_tracker, but track the inverse condition.
+(define_insn "speculation_tracker_rev"
+  [(set (reg:DI SPECULATION_TRACKER_REGNUM)
+	(unspec:DI [(reg:DI SPECULATION_TRACKER_REGNUM) (match_operand 0)]
+	 UNSPEC_SPECULATION_TRACKER_REV))]
+  ""
+  {
+    operands[1] = gen_rtx_REG (DImode, SPECULATION_TRACKER_REGNUM);
+    output_asm_insn ("csel\\t%1, %1, xzr, %M0", operands);
+    return "";
+  }
+  [(set_attr "type" "csel")]
+)
+
 ;; BTI <target> instructions
 (define_insn "bti_noarg"
   [(unspec_volatile [(const_int 0)] UNSPECV_BTI_NOARG)]

gcc/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2020-01-23  Richard Sandiford  <richard.sandiford@arm.com>
+
+	PR target/93341
+	* gcc.target/aarch64/pr93341.c: New test.
+
 2020-01-23  David Malcolm  <dmalcolm@redhat.com>
 
 	* gcc.dg/analyzer/data-model-3.c: Remove hardcoded "-O2" and move

gcc/testsuite/gcc.target/aarch64/pr93341.c

@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-mtrack-speculation" } */
+
+int synths_ ( float * rc)
+{
+  float r1, r2;
+  int i;
+  for (i = 0; i < 128; ++i)
+    {
+      r2 = rc[i];
+      r1 = ((r2) <= (.99f) ? (r2) : (.99f));
+      rc[i] = ((r1) >= (-.99f) ? (r1) : (-.99f));
+    }
+}