re PR middle-end/82004 (SPEC CPU2017 628.pop2_s miscompare)

	PR tree-optimization/82004
	* gimple-match-head.c (optimize_pow_to_exp): New function.
	* match.pd (pow(C,x) -> exp(log(C)*x)): Wrap with #if GIMPLE.
	Don't fold to exp if optimize_pow_to_exp is false.

	* gcc.dg/pr82004.c: New test.

From-SVN: r258930

gcc/ChangeLog

+2018-03-28  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/82004
+	* gimple-match-head.c (optimize_pow_to_exp): New function.
+	* match.pd (pow(C,x) -> exp(log(C)*x)): Wrap with #if GIMPLE.
+	Don't fold to exp if optimize_pow_to_exp is false.
+
 2018-03-28  Martin Liska  <mliska@suse.cz>
 
 	PR other/84819

gcc/gimple-match-head.c

@@ -840,3 +840,71 @@ canonicalize_math_after_vectorization_p ()
 {
   return !cfun || (cfun->curr_properties & PROP_gimple_lvec) != 0;
 }
+
+/* Return true if pow(cst, x) should be optimized into exp(log(cst) * x).
+   As a workaround for SPEC CPU2017 628.pop2_s, don't do it if arg0
+   is an exact integer, arg1 = phi_res +/- cst1 and phi_res = PHI <cst2, ...>
+   where cst2 +/- cst1 is an exact integer, because then pow (arg0, arg1)
+   will likely be exact, while exp (log (arg0) * arg1) might be not.
+   Also don't do it if arg1 is phi_res above and cst2 is an exact integer.  */
+
+static bool
+optimize_pow_to_exp (tree arg0, tree arg1)
+{
+  gcc_assert (TREE_CODE (arg0) == REAL_CST);
+  if (!real_isinteger (TREE_REAL_CST_PTR (arg0), TYPE_MODE (TREE_TYPE (arg0))))
+    return true;
+
+  if (TREE_CODE (arg1) != SSA_NAME)
+    return true;
+
+  gimple *def = SSA_NAME_DEF_STMT (arg1);
+  gphi *phi = dyn_cast <gphi *> (def);
+  tree cst1 = NULL_TREE;
+  enum tree_code code = ERROR_MARK;
+  if (!phi)
+    {
+      if (!is_gimple_assign (def))
+	return true;
+      code = gimple_assign_rhs_code (def);
+      switch (code)
+	{
+	case PLUS_EXPR:
+	case MINUS_EXPR:
+	  break;
+	default:
+	  return true;
+	}
+      if (TREE_CODE (gimple_assign_rhs1 (def)) != SSA_NAME
+	  || TREE_CODE (gimple_assign_rhs2 (def)) != REAL_CST)
+	return true;
+
+      cst1 = gimple_assign_rhs2 (def);
+
+      phi = dyn_cast <gphi *> (SSA_NAME_DEF_STMT (gimple_assign_rhs1 (def)));
+      if (!phi)
+	return true;
+    }
+
+  tree cst2 = NULL_TREE;
+  int n = gimple_phi_num_args (phi);
+  for (int i = 0; i < n; i++)
+    {
+      tree arg = PHI_ARG_DEF (phi, i);
+      if (TREE_CODE (arg) != REAL_CST)
+	continue;
+      else if (cst2 == NULL_TREE)
+	cst2 = arg;
+      else if (!operand_equal_p (cst2, arg, 0))
+	return true;
+    }
+
+  if (cst1 && cst2)
+    cst2 = const_binop (code, TREE_TYPE (cst2), cst2, cst1);
+  if (cst2
+      && TREE_CODE (cst2) == REAL_CST
+      && real_isinteger (TREE_REAL_CST_PTR (cst2),
+			 TYPE_MODE (TREE_TYPE (cst2))))
+    return false;
+  return true;
+}

gcc/match.pd

@@ -4006,6 +4006,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
  /* pow(C,x) -> exp(log(C)*x) if C > 0,
     or if C is a positive power of 2,
     pow(C,x) -> exp2(log2(C)*x).  */
+#if GIMPLE
  (for pows (POW)
       exps (EXP)
       logs (LOG)
@@ -4035,8 +4036,10 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 	 }
      }
      (if (!use_exp2)
-      (exps (mult (logs @0) @1))
+      (if (optimize_pow_to_exp (@0, @1))
+       (exps (mult (logs @0) @1)))
       (exp2s (mult (log2s @0) @1)))))))
+#endif
 
  /* pow(C,x)*expN(y) -> expN(logN(C)*x+y) if C > 0.  */
  (for pows (POW)

gcc/testsuite/ChangeLog

 2018-03-28  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/82004
+	* gcc.dg/pr82004.c: New test.
+
+2018-03-28  Jakub Jelinek  <jakub@redhat.com>
 	    Martin Liska  <mliska@suse.cz>
 
 	PR sanitizer/85081

gcc/testsuite/gcc.dg/pr82004.c

+/* PR tree-optimization/82004 */
+/* { dg-do run } */
+/* { dg-options "-Ofast" } */
+
+extern double log10 (double);
+extern double pow (double, double);
+
+__attribute__((noipa)) void
+bar (double x)
+{
+  if (x < 0.001)
+    __builtin_abort ();
+  asm volatile ("" : : : "memory");
+}
+
+int
+main ()
+{
+  double d = 0.001;
+  double e = 10.0;
+  double f = (log10 (e) - log10 (d)) / 400.0;
+  double g = log10 (d) - f;
+  volatile int q = 0;
+  int i;
+  if (__builtin_expect (q == 0, 0))
+    for (i = 0; i < 400; ++i)
+      {
+	g = g + f;
+	bar (pow (10.0, g));
+      }
+  return 0;  
+}