[PATCH] tree-optimization/107937 - uninit predicate simplification fixup

[PATCH] tree-optimization/107937 - uninit predicate simplification fixup

[Richard Biener]

The following changes the predicate representation to record the
value of a predicate with an empty set of AND predicates.  That's
necessary to properly represent the conservative fallback for the
def vs use predicates.  Since simplification now can result in
such an empty set this distinction becomes important and we need
to check for this as we otherwise ICE.

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

	PR tree-optimization/107937
	* gimple-predicate-analysis.h (predicate::is_true): New.
	(predicate::is_false): Likewise.
	(predicate::empty_val): Likewise.
	(uninit_analysis::uninit_analysis): Properly initialize
	def_preds.
	* gimple-predicate-analysis.cc (simplify_1b): Indicate
	whether the chain became empty.
	(predicate::simplify): Release emptied chain before removing it.
	(predicate::normalize): Replace temporary object with assertion.
	(uninit_analysis::is_use_guarded): Deal with predicates
	that simplify to true/false.

	* gcc.dg/pr107937.c: New testcase.
---
 gcc/gimple-predicate-analysis.cc | 24 +++++++++++++++++++-----
 gcc/gimple-predicate-analysis.h  | 23 ++++++++++++++++++++---
 gcc/testsuite/gcc.dg/pr107937.c  | 24 ++++++++++++++++++++++++
 3 files changed, 63 insertions(+), 8 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/pr107937.c

diff --git a/gcc/gimple-predicate-analysis.cc b/gcc/gimple-predicate-analysis.cc
index ce2e1d10e43..afe01e7f4b8 100644
--- a/gcc/gimple-predicate-analysis.cc
+++ b/gcc/gimple-predicate-analysis.cc
@@ -1249,7 +1249,7 @@ simplify_1a (pred_chain &chain)
 }
 
 /* Implement rule 1b above.  PREDS is the AND predicate to simplify
-   in place.  Returns true if CHAIN simplifies to true.  */
+   in place.  Returns true if CHAIN simplifies to true or false.  */
 
 static bool
 simplify_1b (pred_chain &chain)
@@ -1290,6 +1290,8 @@ simplify_1b (pred_chain &chain)
 	    {
 	      chain.ordered_remove (j);
 	      chain.ordered_remove (i);
+	      if (chain.is_empty ())
+		return true;
 	      i--;
 	      break;
 	    }
@@ -1503,6 +1505,7 @@ predicate::simplify (gimple *use_or_def, bool is_use)
       ::simplify_1a (m_preds[i]);
       if (::simplify_1b (m_preds[i]))
 	{
+	  m_preds[i].release ();
 	  m_preds.ordered_remove (i);
 	  i--;
 	}
@@ -1719,10 +1722,11 @@ predicate::normalize (const pred_chain &chain)
   while (!work_list.is_empty ())
     {
       pred_info pi = work_list.pop ();
-      predicate pred;
       /* The predicate object is not modified here, only NORM_CHAIN and
 	 WORK_LIST are appended to.  */
-      pred.normalize (&norm_chain, pi, BIT_AND_EXPR, &work_list, &mark_set);
+      unsigned oldlen = m_preds.length ();
+      normalize (&norm_chain, pi, BIT_AND_EXPR, &work_list, &mark_set);
+      gcc_assert (m_preds.length () == oldlen);
     }
 
   m_preds.safe_push (norm_chain);
@@ -1740,7 +1744,7 @@ predicate::normalize (gimple *use_or_def, bool is_use)
       dump (dump_file, use_or_def, is_use ? "[USE]:\n" : "[DEF]:\n");
     }
 
-  predicate norm_preds;
+  predicate norm_preds (empty_val ());
   for (unsigned i = 0; i < m_preds.length (); i++)
     {
       if (m_preds[i].length () != 1)
@@ -2076,6 +2080,8 @@ predicate::operator= (const predicate &rhs)
   if (this == &rhs)
     return *this;
 
+  m_cval = rhs.m_cval;
+
   unsigned n = m_preds.length ();
   for (unsigned i = 0; i != n; ++i)
     m_preds[i].release ();
@@ -2204,11 +2210,15 @@ uninit_analysis::is_use_guarded (gimple *use_stmt, basic_block use_bb,
   /* Try to build the predicate expression under which the PHI flows
      into its use.  This will be empty if the PHI is defined and used
      in the same bb.  */
-  predicate use_preds;
+  predicate use_preds (true);
   if (!init_use_preds (use_preds, def_bb, use_bb))
     return false;
 
   use_preds.simplify (use_stmt, /*is_use=*/true);
+  if (use_preds.is_false ())
+    return true;
+  if (use_preds.is_true ())
+    return false;
   use_preds.normalize (use_stmt, /*is_use=*/true);
 
   /* Try to prune the dead incoming phi edges.  */
@@ -2227,6 +2237,10 @@ uninit_analysis::is_use_guarded (gimple *use_stmt, basic_block use_bb,
 	return false;
 
       m_phi_def_preds.simplify (phi);
+      if (m_phi_def_preds.is_false ())
+	return false;
+      if (m_phi_def_preds.is_true ())
+	return true;
       m_phi_def_preds.normalize (phi);
     }
 
diff --git a/gcc/gimple-predicate-analysis.h b/gcc/gimple-predicate-analysis.h
index 972af5e0b2d..c4a7ed51967 100644
--- a/gcc/gimple-predicate-analysis.h
+++ b/gcc/gimple-predicate-analysis.h
@@ -45,7 +45,7 @@ class predicate
 {
  public:
   /* Construct with the specified EVAL object.  */
-  predicate () : m_preds (vNULL) { }
+  predicate (bool empty_val) : m_preds (vNULL), m_cval (empty_val) { }
 
   /* Copy.  */
   predicate (const predicate &rhs) : m_preds (vNULL) { *this = rhs; }
@@ -60,6 +60,21 @@ class predicate
     return m_preds.is_empty ();
   }
 
+  bool is_true () const
+  {
+    return is_empty () && m_cval;
+  }
+
+  bool is_false () const
+  {
+    return is_empty () && !m_cval;
+  }
+
+  bool empty_val () const
+  {
+    return m_cval;
+  }
+
   const pred_chain_union chain () const
   {
     return m_preds;
@@ -92,8 +107,10 @@ private:
   bool simplify_3 ();
   bool simplify_4 ();
 
-  /* Representation of the predicate expression(s).  */
+  /* Representation of the predicate expression(s).  The predicate is
+     m_cval || m_preds[0] || ...  */
   pred_chain_union m_preds;
+  bool m_cval;
 };
 
 /* Represents a complex Boolean predicate expression.  */
@@ -119,7 +136,7 @@ class uninit_analysis
 
   /* Construct with the specified EVAL object.  */
   uninit_analysis (func_t &eval)
-    : m_phi_def_preds (), m_eval (eval) { }
+    : m_phi_def_preds (false), m_eval (eval) { }
 
   /* Copy.  */
   uninit_analysis (const uninit_analysis &rhs) = delete;
diff --git a/gcc/testsuite/gcc.dg/pr107937.c b/gcc/testsuite/gcc.dg/pr107937.c
new file mode 100644
index 00000000000..524850bcfa5
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr107937.c
@@ -0,0 +1,24 @@
+/* { dg-do compile } */
+/* { dg-options "-O -Wuninitialized" } */
+
+int _setjmp(int);
+int regs, vm_debug_engine_vp_0, vm_debug_engine_vp_2;
+
+void
+vm_dispatch_hook();
+
+
+void
+vm_debug_engine() {
+  int fp;
+  void *jump_table = &&l_nop;
+l_nop:
+  if (__builtin_expect(vm_debug_engine_vp_2, 0))
+    vm_dispatch_hook();
+  if (_setjmp(regs)) {
+    fp = fp;
+    vm_dispatch_hook();
+    goto *jump_table;
+  }
+  vm_debug_engine_vp_0 = fp;
+}
-- 
2.35.3