[PR80693] drop value of parallel SETs dropped by combine

When combine drops a REG_UNUSED SET in a parallel, we have to clear
cached values, so that, even if the REGs remain used (e.g. because
they were referenced in the used SET_SRC), we will not use properties
of the dropped modified value as if they applied to the preserved
original one.

We fail to adjust REG_N_SETS.

for  gcc/ChangeLog

	PR rtl-optimization/80693
	PR rtl-optimization/81019
	PR rtl-optimization/81020
	* combine.c (distribute_notes): Reset any REG_UNUSED REGs that
	are not mentioned in i3.  Place the REG_UNUSED note on i2,
	possibly modified to REG_DEAD, if it did not originate in i3.

for  gcc/testsuite/ChangeLog

	PR rtl-optimization/80693
	PR rtl-optimization/81019
	PR rtl-optimization/81020
	* gcc.dg/pr80693.c: New.
	* gcc.dg/pr81019.c: New.

From-SVN: r255554

5 files changed, 110 insertions, 0 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index bd41af8..04fbd66 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,12 @@
+2017-12-11  Alexandre Oliva <aoliva@redhat.com>
+
+	PR rtl-optimization/80693
+	PR rtl-optimization/81019
+	PR rtl-optimization/81020
+	* combine.c (distribute_notes): Reset any REG_UNUSED REGs that
+	are not mentioned in i3.  Place the REG_UNUSED note on i2,
+	possibly modified to REG_DEAD, if it did not originate in i3.
+
 2017-12-11  Jakub Jelinek  <jakub@redhat.com>
 
 	* recog.c (store_data_bypass_p_1): New function.
diff --git a/gcc/combine.c b/gcc/combine.c
index 786a840..7f10c67 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -14219,6 +14219,46 @@ distribute_notes (rtx notes, rtx_insn *from_insn, rtx_insn *i3, rtx_insn *i2,
 	      PUT_REG_NOTE_KIND (note, REG_DEAD);
 	      place = i3;
 	    }
+
+	  /* A SET or CLOBBER of the REG_UNUSED reg has been removed,
+	     but we can't tell which at this point.  We must reset any
+	     expectations we had about the value that was previously
+	     stored in the reg.  ??? Ideally, we'd adjust REG_N_SETS
+	     and, if appropriate, restore its previous value, but we
+	     don't have enough information for that at this point.  */
+	  else
+	    {
+	      record_value_for_reg (XEXP (note, 0), NULL, NULL_RTX);
+
+	      /* Otherwise, if this register is now referenced in i2
+		 then the register used to be modified in one of the
+		 original insns.  If it was i3 (say, in an unused
+		 parallel), it's now completely gone, so the note can
+		 be discarded.  But if it was modified in i2, i1 or i0
+		 and we still reference it in i2, then we're
+		 referencing the previous value, and since the
+		 register was modified and REG_UNUSED, we know that
+		 the previous value is now dead.  So, if we only
+		 reference the register in i2, we change the note to
+		 REG_DEAD, to reflect the previous value.  However, if
+		 we're also setting or clobbering the register as
+		 scratch, we know (because the register was not
+		 referenced in i3) that it's unused, just as it was
+		 unused before, and we place the note in i2.  */
+	      if (from_insn != i3 && i2 && INSN_P (i2)
+		  && reg_referenced_p (XEXP (note, 0), PATTERN (i2)))
+		{
+		  if (!reg_set_p (XEXP (note, 0), PATTERN (i2)))
+		    PUT_REG_NOTE_KIND (note, REG_DEAD);
+		  if (! (REG_P (XEXP (note, 0))
+			 ? find_regno_note (i2, REG_NOTE_KIND (note),
+					    REGNO (XEXP (note, 0)))
+			 : find_reg_note (i2, REG_NOTE_KIND (note),
+					  XEXP (note, 0))))
+		    place = i2;
+		}
+	    }
+
 	  break;
 
 	case REG_EQUAL:
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 3c2f0d2..5cdd493 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,11 @@
+2017-12-11  Alexandre Oliva <aoliva@redhat.com>
+
+	PR rtl-optimization/80693
+	PR rtl-optimization/81019
+	PR rtl-optimization/81020
+	* gcc.dg/pr80693.c: New.
+	* gcc.dg/pr81019.c: New.
+
 2017-12-11  Segher Boessenkool  <segher@kernel.crashing.org>
 
 	PR rtl-optimization/83361
diff --git a/gcc/testsuite/gcc.dg/pr80693.c b/gcc/testsuite/gcc.dg/pr80693.c
new file mode 100644
index 0000000..5071771
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr80693.c
@@ -0,0 +1,26 @@
+/* { dg-do run } */
+/* { dg-options "-O -fno-tree-coalesce-vars" } */
+typedef unsigned char u8;
+typedef unsigned short u16;
+typedef unsigned u32;
+typedef unsigned long long u64;
+
+static u64 __attribute__((noinline, noclone))
+foo(u8 u8_0, u16 u16_0, u32 u32_0, u64 u64_0,  u16 u16_1)
+{
+  u16_1 += 0x1051;
+  u16_1 &= 1;
+  u8_0 <<= u32_0 & 7;
+  u16_0 -= !u16_1;
+  u16_1 >>= ((u16)-u8_0 != 0xff);
+  return u8_0 + u16_0 + u64_0 + u16_1;
+}
+
+int
+main (void)
+{
+  u64 x = foo(1, 1, 0xffff, 0, 1);
+  if (x != 0x80)
+    __builtin_abort();
+  return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/pr81019.c b/gcc/testsuite/gcc.dg/pr81019.c
new file mode 100644
index 0000000..cf13bfa
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr81019.c
@@ -0,0 +1,27 @@
+/* PR rtl-optimization/81019 */
+/* { dg-do run } */
+/* { dg-options "-O -fno-tree-ccp" } */
+
+unsigned long long __attribute__((noinline, noclone))
+foo (unsigned char a, unsigned short b, unsigned c, unsigned long long d,
+     unsigned char e, unsigned short f, unsigned g, unsigned long long h)
+{
+  g = e;
+  c &= 0 < d;
+  b *= d;
+  g ^= -1;
+  g &= 1;
+  c |= 1;
+  a -= 0 < g;
+  g >>= 1;
+  f = b | (f >> b);
+  return a + c + d + f + g + h;
+}
+
+int
+main (void)
+{
+  if (foo (0, 0, 0, 0, 0, 0, 0, 0) != 0x100)
+    __builtin_abort ();
+  return 0;
+}