[gcc r14-4329] tree-optimization/111583 - loop distribution issue

[Richard Biener]

https://gcc.gnu.org/g:962ca7149d652e4077a2259886e5cd2ea3cea0ab

commit r14-4329-g962ca7149d652e4077a2259886e5cd2ea3cea0ab
Author: Richard Biener <rguenther@suse.de>
Date:   Fri Sep 29 11:08:18 2023 +0200

    tree-optimization/111583 - loop distribution issue
    
    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.
    
            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.

Diff:
---
 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(+)

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)