[5/n][PR rtl-optimization/115877] Fix handling of input/output operands

So in this patch we're correcting a failure to mark objects live in scenarios
like

(set (dest) (plus (dest) (src))

When handling set pseudos, we transfer the liveness information from LIVENOW
into LIVE_TMP.  LIVE_TMP is subsequently used to narrow what bit groups are
live for the inputs.

The first time we process the block we may not have DEST in the LIVENOW set (it
may be live across the loop, but not live after the loop).  Thus we can totally
miss making certain objects live, resulting in incorrect code.

The fix is pretty simple.  If LIVE_TMP is empty, then we should go ahead and
mark all the bit groups for the set object in LIVE_TMP.  This also removes an
invalid gcc_assert on the state of the liveness bitmaps.

This showed up on pru, rl78 and/or msp430 in the testsuite.  So no new test.

Bootstrapped and regression tested on x86_64 and also run through my tester on
all the cross platforms.

Pushing to the trunk.

	PR rtl-optimization/115877
gcc/
	* ext-dce.cc (ext_dce_process_sets): Reasonably handle input/output
	operands.
	(ext_dce_rd_transfer_n): Drop bogus assertion.

1 files changed, 26 insertions, 5 deletions

diff --git a/gcc/ext-dce.cc b/gcc/ext-dce.cc
index 21feabd..c56dfb5 100644
--- a/gcc/ext-dce.cc
+++ b/gcc/ext-dce.cc
@@ -245,13 +245,25 @@ ext_dce_process_sets (rtx_insn *insn, rtx obj, bitmap live_tmp)
 		  continue;
 		}
 
-	      /* Transfer all the LIVENOW bits for X into LIVE_TMP.  */
+	      /* LIVE_TMP contains the set groups that are live-out and set in
+		 this insn.  It is used to narrow the groups live-in for the
+		 inputs of this insn.
+
+		 The simple thing to do is mark all the groups as live, but
+		 that will significantly inhibit optimization.
+
+		 We also need to be careful in the case where we have an in-out
+		 operand.  If we're not careful we'd clear LIVE_TMP
+		 incorrectly.  */
 	      HOST_WIDE_INT rn = REGNO (SUBREG_REG (x));
 	      int limit = group_limit (SUBREG_REG (x));
 	      for (HOST_WIDE_INT i = 4 * rn; i < 4 * rn + limit; i++)
 		if (bitmap_bit_p (livenow, i))
 		  bitmap_set_bit (live_tmp, i);
 
+	      if (bitmap_empty_p (live_tmp))
+		make_reg_live (live_tmp, rn);
+
 	      /* The mode of the SUBREG tells us how many bits we can
 		 clear.  */
 	      machine_mode mode = GET_MODE (x);
@@ -316,14 +328,25 @@ ext_dce_process_sets (rtx_insn *insn, rtx obj, bitmap live_tmp)
 	  /* Now handle the actual object that was changed.  */
 	  if (REG_P (x))
 	    {
-	      /* Transfer the appropriate bits from LIVENOW into
-		 LIVE_TMP.  */
+	      /* LIVE_TMP contains the set groups that are live-out and set in
+		 this insn.  It is used to narrow the groups live-in for the
+		 inputs of this insn.
+
+		 The simple thing to do is mark all the groups as live, but
+		 that will significantly inhibit optimization.
+
+		 We also need to be careful in the case where we have an in-out
+		 operand.  If we're not careful we'd clear LIVE_TMP
+		 incorrectly.  */
 	      HOST_WIDE_INT rn = REGNO (x);
 	      int limit = group_limit (x);
 	      for (HOST_WIDE_INT i = 4 * rn; i < 4 * rn + limit; i++)
 		if (bitmap_bit_p (livenow, i))
 		  bitmap_set_bit (live_tmp, i);
 
+	      if (bitmap_empty_p (live_tmp))
+		make_reg_live (live_tmp, rn);
+
 	      /* Now clear the bits known written by this instruction.
 		 Note that BIT need not be a power of two, consider a
 		 ZERO_EXTRACT destination.  */
@@ -935,8 +958,6 @@ ext_dce_rd_transfer_n (int bb_index)
      the generic dataflow code that something changed.  */
   if (!bitmap_equal_p (&livein[bb_index], livenow))
     {
-      gcc_assert (!bitmap_intersect_compl_p (&livein[bb_index], livenow));
-
       bitmap_copy (&livein[bb_index], livenow);
       return true;
     }