vrp: Fix up gcc.target/aarch64/pr90838.c [PR97312, PR94801]

> Perhaps another way out of this would be document and enforce that
> __builtin_c[lt]z{,l,ll} etc calls are undefined at zero, but C[TL]Z ifn
> calls are defined there based on *_DEFINED_VALUE_AT_ZERO (*) == 2

The following patch implements that, i.e. __builtin_c?z* now take full
advantage of them being UB at zero, while the ifns are well defined at zero
if *_DEFINED_VALUE_AT_ZERO (*) == 2.  That is what fixes PR94801.

Furthermore, to fix PR97312, if it is well defined at zero and the value at
zero is prec, we don't lower the maximum unless the argument is known to be
non-zero.
For gimple-range.cc I guess we could improve it if needed e.g. by returning
a [0,7][32,32] range for .CTZ of e.g. [0,137], but for now it (roughly)
matches what vr-values.c does.

2020-10-09  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/94801
	PR target/97312
	* vr-values.c (vr_values::extract_range_basic) <CASE_CFN_CLZ,
	CASE_CFN_CTZ>: When stmt is not an internal-fn call or
	C?Z_DEFINED_VALUE_AT_ZERO is not 2, assume argument is not zero
	and thus use [0, prec-1] range unless it can be further improved.
	For CTZ, don't update maxi from upper bound if it was previously prec.
	* gimple-range.cc (gimple_ranger::range_of_builtin_call) <CASE_CFN_CLZ,
	CASE_CFN_CTZ>: Likewise.

	* gcc.dg/tree-ssa/pr94801.c: New test.

1 files changed, 57 insertions, 35 deletions

diff --git a/gcc/vr-values.c b/gcc/vr-values.c
index 88aa672..da0b249 100644
--- a/gcc/vr-values.c
+++ b/gcc/vr-values.c
@@ -1208,34 +1208,42 @@ vr_values::extract_range_basic (value_range_equiv *vr, gimple *stmt)
 	  mini = 0;
 	  maxi = 1;
 	  goto bitop_builtin;
-	  /* __builtin_c[lt]z* return [0, prec-1], except for
+	  /* __builtin_clz* return [0, prec-1], except for
 	     when the argument is 0, but that is undefined behavior.
-	     On many targets where the CLZ RTL or optab value is defined
-	     for 0 the value is prec, so include that in the range
-	     by default.  */
+	     Always handle __builtin_clz* which can be only written
+	     by user as UB on 0 and so [0, prec-1] range, and the internal-fn
+	     calls depending on how CLZ_DEFINED_VALUE_AT_ZERO is defined.  */
 	CASE_CFN_CLZ:
 	  arg = gimple_call_arg (stmt, 0);
 	  prec = TYPE_PRECISION (TREE_TYPE (arg));
 	  mini = 0;
-	  maxi = prec;
+	  maxi = prec - 1;
 	  mode = SCALAR_INT_TYPE_MODE (TREE_TYPE (arg));
-	  if (optab_handler (clz_optab, mode) != CODE_FOR_nothing
-	      && CLZ_DEFINED_VALUE_AT_ZERO (mode, zerov)
-	      /* Handle only the single common value.  */
-	      && zerov != prec)
-	    /* Magic value to give up, unless vr0 proves
-	       arg is non-zero.  */
-	    mini = -2;
+	  if (gimple_call_internal_p (stmt))
+	    {
+	      if (optab_handler (clz_optab, mode) != CODE_FOR_nothing
+		  && CLZ_DEFINED_VALUE_AT_ZERO (mode, zerov) == 2)
+		{
+		  /* Handle only the single common value.  */
+		  if (zerov == prec)
+		    maxi = prec;
+		  /* Magic value to give up, unless vr0 proves
+		     arg is non-zero.  */
+		  else
+		    mini = -2;
+		}
+	    }
 	  if (TREE_CODE (arg) == SSA_NAME)
 	    {
 	      const value_range_equiv *vr0 = get_value_range (arg);
 	      /* From clz of VR_RANGE minimum we can compute
 		 result maximum.  */
 	      if (vr0->kind () == VR_RANGE
-		  && TREE_CODE (vr0->min ()) == INTEGER_CST)
+		  && TREE_CODE (vr0->min ()) == INTEGER_CST
+		  && integer_nonzerop (vr0->min ()))
 		{
 		  maxi = prec - 1 - tree_floor_log2 (vr0->min ());
-		  if (maxi != prec)
+		  if (mini == -2)
 		    mini = 0;
 		}
 	      else if (vr0->kind () == VR_ANTI_RANGE
@@ -1251,9 +1259,14 @@ vr_values::extract_range_basic (value_range_equiv *vr, gimple *stmt)
 	      if (vr0->kind () == VR_RANGE
 		  && TREE_CODE (vr0->max ()) == INTEGER_CST)
 		{
-		  mini = prec - 1 - tree_floor_log2 (vr0->max ());
-		  if (mini == prec)
-		    break;
+		  int newmini = prec - 1 - tree_floor_log2 (vr0->max ());
+		  if (newmini == prec)
+		    {
+		      if (maxi == prec)
+			mini = prec;
+		    }
+		  else
+		    mini = newmini;
 		}
 	    }
 	  if (mini == -2)
@@ -1261,27 +1274,30 @@ vr_values::extract_range_basic (value_range_equiv *vr, gimple *stmt)
 	  goto bitop_builtin;
 	  /* __builtin_ctz* return [0, prec-1], except for
 	     when the argument is 0, but that is undefined behavior.
-	     If there is a ctz optab for this mode and
-	     CTZ_DEFINED_VALUE_AT_ZERO, include that in the range,
-	     otherwise just assume 0 won't be seen.  */
+	     Always handle __builtin_ctz* which can be only written
+	     by user as UB on 0 and so [0, prec-1] range, and the internal-fn
+	     calls depending on how CTZ_DEFINED_VALUE_AT_ZERO is defined.  */
 	CASE_CFN_CTZ:
 	  arg = gimple_call_arg (stmt, 0);
 	  prec = TYPE_PRECISION (TREE_TYPE (arg));
 	  mini = 0;
 	  maxi = prec - 1;
 	  mode = SCALAR_INT_TYPE_MODE (TREE_TYPE (arg));
-	  if (optab_handler (ctz_optab, mode) != CODE_FOR_nothing
-	      && CTZ_DEFINED_VALUE_AT_ZERO (mode, zerov))
+	  if (gimple_call_internal_p (stmt))
 	    {
-	      /* Handle only the two common values.  */
-	      if (zerov == -1)
-		mini = -1;
-	      else if (zerov == prec)
-		maxi = prec;
-	      else
-		/* Magic value to give up, unless vr0 proves
-		   arg is non-zero.  */
-		mini = -2;
+	      if (optab_handler (ctz_optab, mode) != CODE_FOR_nothing
+		  && CTZ_DEFINED_VALUE_AT_ZERO (mode, zerov) == 2)
+		{
+		  /* Handle only the two common values.  */
+		  if (zerov == -1)
+		    mini = -1;
+		  else if (zerov == prec)
+		    maxi = prec;
+		  else
+		    /* Magic value to give up, unless vr0 proves
+		       arg is non-zero.  */
+		    mini = -2;
+		}
 	    }
 	  if (TREE_CODE (arg) == SSA_NAME)
 	    {
@@ -1300,10 +1316,16 @@ vr_values::extract_range_basic (value_range_equiv *vr, gimple *stmt)
 	      if (vr0->kind () == VR_RANGE
 		  && TREE_CODE (vr0->max ()) == INTEGER_CST)
 		{
-		  maxi = tree_floor_log2 (vr0->max ());
-		  /* For vr0 [0, 0] give up.  */
-		  if (maxi == -1)
-		    break;
+		  int newmaxi = tree_floor_log2 (vr0->max ());
+		  if (newmaxi == -1)
+		    {
+		      if (mini == -1)
+			maxi = -1;
+		      else if (maxi == prec)
+			mini = prec;
+		    }
+		  else if (maxi != prec)
+		    maxi = newmaxi;
 		}
 	    }
 	  if (mini == -2)