diff mbox series

tree-optimization/111583 - loop distribution issue

Message ID 20230929095001.3ABB91390A@imap2.suse-dmz.suse.de
State Accepted
Headers
Series tree-optimization/111583 - loop distribution issue |

Checks

Context Check Description
snail/gcc-patch-check success Github commit url

Commit Message

Richard Biener Sept. 29, 2023, 9:50 a.m. UTC 
  The following conservatively fixes loop distribution to only
recognize memset/memcpy and friends when at least one element
is going to be processed.  This avoids having an unconditional
builtin call in the IL that might imply the source and destination
pointers are non-NULL when originally pointers were not always
dereferenced.

With -Os loop header copying is less likely to ensure this.

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.

	PR tree-optimization/111583
	* tree-loop-distribution.cc (find_single_drs): Ensure the
	load/store are always executed.

	* gcc.dg/tree-ssa/pr111583-1.c: New testcase.
	* gcc.dg/tree-ssa/pr111583-2.c: Likewise.
---
 gcc/testsuite/gcc.dg/tree-ssa/pr111583-1.c | 30 ++++++++++++++++++
 gcc/testsuite/gcc.dg/tree-ssa/pr111583-2.c | 36 ++++++++++++++++++++++
 gcc/tree-loop-distribution.cc              | 15 +++++++++
 3 files changed, 81 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr111583-1.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr111583-2.c
diff mbox series

Patch

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr111583-1.c b/gcc/testsuite/gcc.dg/tree-ssa/pr111583-1.c
new file mode 100644
index 00000000000..1dd8dbcf1d8
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr111583-1.c
@@ -0,0 +1,30 @@ 
+/* { dg-do run } */
+/* { dg-options "-Os" } */
+
+short a, f, i;
+static const int *e;
+short *g;
+long h;
+int main()
+{
+    {
+      unsigned j = i;
+      a = 1;
+      for (; a; a++) {
+	    {
+	      long b = j, d = h;
+	      int c = 0;
+	      while (d--)
+		*(char *)b++ = c;
+	    }
+	  if (e)
+	    break;
+      }
+      j && (*g)--;
+      const int **k = &e;
+      *k = 0;
+    }
+  if (f != 0)
+    __builtin_abort ();
+  return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr111583-2.c b/gcc/testsuite/gcc.dg/tree-ssa/pr111583-2.c
new file mode 100644
index 00000000000..0ee21854552
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr111583-2.c
@@ -0,0 +1,36 @@ 
+/* { dg-do run } */
+/* { dg-options "-Os" } */
+
+int b, c, d;
+char e;
+short f;
+const unsigned short **g;
+char h(char k) {
+  if (k)
+    return '0';
+  return 0;
+}
+int l() {
+  b = 0;
+  return 1;
+}
+static short m(unsigned k) {
+  const unsigned short *n[65];
+  g = &n[4];
+  k || l();
+  long a = k;
+  char i = 0;
+  unsigned long j = k;
+  while (j--)
+    *(char *)a++ = i;
+  c = h(d);
+  f = k;
+  return 0;
+}
+int main() {
+  long o = (e < 0) << 5;
+  m(o);
+  if (f != 0)
+    __builtin_abort ();
+  return 0;
+}
diff --git a/gcc/tree-loop-distribution.cc b/gcc/tree-loop-distribution.cc
index a28470b66ea..39fd4402d25 100644
--- a/gcc/tree-loop-distribution.cc
+++ b/gcc/tree-loop-distribution.cc
@@ -1574,6 +1574,7 @@  find_single_drs (class loop *loop, struct graph *rdg, const bitmap &partition_st
 
   basic_block bb_ld = NULL;
   basic_block bb_st = NULL;
+  edge exit = single_exit (loop);
 
   if (single_ld)
     {
@@ -1589,6 +1590,14 @@  find_single_drs (class loop *loop, struct graph *rdg, const bitmap &partition_st
       bb_ld = gimple_bb (DR_STMT (single_ld));
       if (!dominated_by_p (CDI_DOMINATORS, loop->latch, bb_ld))
 	return false;
+
+      /* The data reference must also be executed before possibly exiting
+	 the loop as otherwise we'd for example unconditionally execute
+	 memset (ptr, 0, n) which even with n == 0 implies ptr is non-NULL.  */
+      if (bb_ld != loop->header
+	  && (!exit
+	      || !dominated_by_p (CDI_DOMINATORS, exit->src, bb_ld)))
+	return false;
     }
 
   if (single_st)
@@ -1604,6 +1613,12 @@  find_single_drs (class loop *loop, struct graph *rdg, const bitmap &partition_st
       bb_st = gimple_bb (DR_STMT (single_st));
       if (!dominated_by_p (CDI_DOMINATORS, loop->latch, bb_st))
 	return false;
+
+      /* And before exiting the loop.  */
+      if (bb_st != loop->header
+	  && (!exit
+	      || !dominated_by_p (CDI_DOMINATORS, exit->src, bb_st)))
+	return false;
     }
 
   if (single_ld && single_st)