rtlanal: Treat writes to sp as also writing to memory [PR117938]

This PR was about a case in which late-combine moved a stack
deallocation across an earlier stack access.  This was possible
because the deallocation was missing the RTL-SSA equivalent of
a vop, which in turn was because rtl_properties didn't treat
the deallocation as writing to memory.  I think the bug was
ultimately there.

gcc/
	PR rtl-optimization/117938
	* rtlanal.cc (rtx_properties::try_to_add_dest): Treat writes
	to the stack pointer as also writing to memory.

gcc/testsuite/
	PR rtl-optimization/117938
	* gcc.dg/torture/pr117938.c: New test.

2 files changed, 47 insertions, 3 deletions

diff --git a/gcc/rtlanal.cc b/gcc/rtlanal.cc
index e7efb48..8caffaf 100644
--- a/gcc/rtlanal.cc
+++ b/gcc/rtlanal.cc
@@ -2163,10 +2163,18 @@ rtx_properties::try_to_add_dest (const_rtx x, unsigned int flags)
 
   if (LIKELY (REG_P (x)))
     {
-      /* We want to keep sp alive everywhere -  by making all
-	 writes to sp also use sp. */
       if (REGNO (x) == STACK_POINTER_REGNUM)
-	flags |= rtx_obj_flags::IS_READ;
+	{
+	  /* Stack accesses are dependent on previous allocations and
+	     anti-dependent on later deallocations, so both types of
+	     stack operation are akin to a memory write.  */
+	  if (ref_iter != ref_end)
+	    *ref_iter++ = rtx_obj_reference (MEM_REGNO, flags, BLKmode);
+
+	  /* We want to keep sp alive everywhere - by making all
+	     writes to sp also use sp.  */
+	  flags |= rtx_obj_flags::IS_READ;
+	}
       try_to_add_reg (x, flags);
       return;
     }
diff --git a/gcc/testsuite/gcc.dg/torture/pr117938.c b/gcc/testsuite/gcc.dg/torture/pr117938.c
new file mode 100644
index 0000000..5a3b6d2
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr117938.c
@@ -0,0 +1,36 @@
+/* { dg-do run { target { int32 && int128 } } } */
+/* { dg-additional-options "-Wno-psabi --param=max-cse-insns=1" } */
+
+typedef unsigned V __attribute__((__vector_size__(64)));
+typedef unsigned __int128 W __attribute__((__vector_size__(64)));
+unsigned a;
+W b;
+V c;
+W d;
+
+__attribute__((__noinline__))
+W
+bar (unsigned u, V z, W w)
+{
+  u *= z[5];
+  return u + w;
+}
+
+W
+foo (V v)
+{
+  unsigned g = a ? 1 : -1;
+  v ^= 0 <= v;
+  v <<= ((V){ bar (0, c, b)[0] } & 1);
+  v >>= ((V){ g, bar (1, c, b)[0] } & 1);
+  return a + b + (W) v + d;
+}
+
+int
+main ()
+{
+  V x = (V) foo ((V) { });
+  for (unsigned i = 0; i < sizeof(x)/sizeof(x[0]); i++)
+    if (x[i] != (i ? 0xffffffff : 0x7fffffff))
+      __builtin_abort();
+}