Re: [PATCH 2/2] Enable elimination of zext/sext

[Kugan <kugan.vivekanandarajah@linaro.org>]

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On 06/08/14 23:29, Richard Biener wrote:
> On Wed, Aug 6, 2014 at 3:21 PM, Kugan <kugan.vivekanandarajah@linaro.org> wrote:
>> On 06/08/14 22:09, Richard Biener wrote:
>>> On Tue, Aug 5, 2014 at 4:21 PM, Jakub Jelinek <jakub@redhat.com> wrote:
>>>> On Tue, Aug 05, 2014 at 04:17:41PM +0200, Richard Biener wrote:
>>>>> what's the semantic of setting SRP_SIGNED_AND_UNSIGNED
>>>>> on the subreg?  That is, for the created (subreg:lhs_mode
>>>>> (reg:<PROMOTE_MODE of ssa> N))?
>>>>
>>>> SRP_SIGNED_AND_UNSIGNED on a subreg should mean that
>>>> the subreg is both zero and sign extended, which means
>>>> that the topmost bit of the narrower mode is known to be zero,
>>>> and all bits above it in the wider mode are known to be zero too.
>>>> SRP_SIGNED means that the topmost bit of the narrower mode is
>>>> either 0 or 1 and depending on that the above wider mode bits
>>>> are either all 0 or all 1.
>>>> SRP_UNSIGNED means that regardless of the topmost bit value,
>>>> all above wider mode bits are 0.
>>>
>>> Ok, then from the context of the patch we already know that
>>> either SRP_UNSIGNED or SRP_SIGNED is true which means
>>> that the value is sign- or zero-extended.
>>>
>>> I suppose inside promoted_for_type_p
>>> TYPE_MODE (TREE_TYPE (ssa)) == lhs_mode, I'm not sure
>>> why you pass !unsignedp as lhs_uns.
>>
>> In expand_expr_real_1, it is already known that it is promoted for
>> unsigned_p and we are setting SUBREG_PROMOTED_SET (temp, unsignedp).
>>
>> If we can prove that it is also promoted for !unsignedp, we can set
>> SUBREG_PROMOTED_SET (temp, SRP_SIGNED_AND_UNSIGNED).
>>
>> promoted_for_type_p should prove this based on the value range info.
>>
>>>
>>> Now, from 'ssa' alone we can't tell anything about a larger mode
>>> registers value if that is either zero- or sign-extended.  But we
>>> know that those bits are properly zero-extended if unsignedp
>>> and properly sign-extended if !unsignedp?
>>>
>>> So what the predicate tries to prove is that sign- and zero-extending
>>> results in the same larger-mode value.  This is true if the
>>> MSB of the smaller mode is not set.
>>>
>>> Let's assume that smaller mode is that of 'ssa' then the test
>>> is just
>>>
>>>   return (!tree_int_cst_sign_bit (min) && !tree_int_cst_sign_bit (max));
>>>
>>> no?
>>
>> hmm,  is this because we will never have a call to promoted_for_type_p
>> with same sign (ignoring PROMOTE_MODE) for 'ssa' and the larger mode.
>> The case with larger mode signed and 'ssa' unsigned will not work.
>> Therefore larger mode unsigned and 'ssa' signed will be the only case
>> that we should consider.
>>
>> However, with PROMOTE_MODE, isnt that we will miss some cases with this.
> 
> No, PROMOTE_MODE will still either sign- or zero-extend.  If either
> results in zeros in the upper bits then PROMOTE_MODE doesn't matter.
> 

Thanks for the explanation. Please find the attached patch that
implements this. I have updated the comments and predicate to match this.

Bootstrap tested on x86_64-unknown-linux-gnu and regression tested on
x86_64-unknown-linux-gnu and arm-none-linux-gnueabi with no new
regressions. Is this OK?

Thanks,
Kugan

gcc/
2014-08-07  Kugan Vivekanandarajah  <kuganv@linaro.org>

	* calls.c (precompute_arguments): Check
	 promoted_for_signed_and_unsigned_p and set the promoted mode.
	(promoted_for_signed_and_unsigned_p): New function.
	(expand_expr_real_1): Check promoted_for_signed_and_unsigned_p
	and set the promoted mode.
	* expr.h (promoted_for_signed_and_unsigned_p): New function definition.
	* cfgexpand.c (expand_gimple_stmt_1): Call emit_move_insn if
	SUBREG is promoted with SRP_SIGNED_AND_UNSIGNED.


gcc/testsuite
2014-08-07  Kugan Vivekanandarajah  <kuganv@linaro.org>

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



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diff --git a/gcc/calls.c b/gcc/calls.c
index 00c5028..4285ec1 100644
--- a/gcc/calls.c
+++ b/gcc/calls.c
@@ -1484,7 +1484,10 @@ precompute_arguments (int num_actuals, struct arg_data *args)
 	      args[i].initial_value
 		= gen_lowpart_SUBREG (mode, args[i].value);
 	      SUBREG_PROMOTED_VAR_P (args[i].initial_value) = 1;
-	      SUBREG_PROMOTED_SET (args[i].initial_value, args[i].unsignedp);
+	      if (promoted_for_signed_and_unsigned_p (args[i].tree_value, mode))
+		SUBREG_PROMOTED_SET (args[i].initial_value, SRP_SIGNED_AND_UNSIGNED);
+	      else
+		SUBREG_PROMOTED_SET (args[i].initial_value, args[i].unsignedp);
 	    }
 	}
     }
diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
index f98c322..b14626c 100644
--- a/gcc/cfgexpand.c
+++ b/gcc/cfgexpand.c
@@ -3309,7 +3309,13 @@ expand_gimple_stmt_1 (gimple stmt)
 					  GET_MODE (target), temp, unsignedp);
 		  }
 
-		convert_move (SUBREG_REG (target), temp, unsignedp);
+		if ((SUBREG_PROMOTED_GET (target) == SRP_SIGNED_AND_UNSIGNED)
+		    && (GET_CODE (temp) == SUBREG)
+		    && (GET_MODE (target) == GET_MODE (temp))
+		    && (GET_MODE (SUBREG_REG (target)) == GET_MODE (SUBREG_REG (temp))))
+		  emit_move_insn (SUBREG_REG (target), SUBREG_REG (temp));
+		else
+		  convert_move (SUBREG_REG (target), temp, unsignedp);
 	      }
 	    else if (nontemporal && emit_storent_insn (target, temp))
 	      ;
diff --git a/gcc/expr.c b/gcc/expr.c
index 1242031..c217b9a 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -68,6 +68,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "tree-ssa-address.h"
 #include "cfgexpand.h"
 #include "builtins.h"
+#include "tree-ssa.h"
 
 #ifndef STACK_PUSH_CODE
 #ifdef STACK_GROWS_DOWNWARD
@@ -9224,6 +9225,35 @@ expand_expr_real_2 (sepops ops, rtx target, enum machine_mode tmode,
 }
 #undef REDUCE_BIT_FIELD
 
+/* Return TRUE if value in SSA is zero and sign extended for wider mode MODE
+   using value range information stored.  Return FALSE otherwise.
+
+   This is used to check if SUBREG is zero and sign extended and to set
+   promoted mode SRP_SIGNED_AND_UNSIGNED to SUBREG.  */
+
+bool
+promoted_for_signed_and_unsigned_p (tree ssa, enum machine_mode mode)
+{
+  wide_int min, max;
+
+  if (ssa == NULL_TREE
+      || TREE_CODE (ssa) != SSA_NAME
+      || !INTEGRAL_TYPE_P (TREE_TYPE (ssa))
+      || (TYPE_PRECISION (TREE_TYPE (ssa)) > GET_MODE_PRECISION (mode)))
+    return false;
+
+  /* Return FALSE if value_range is not recorded for SSA.  */
+  if (get_range_info (ssa, &min, &max) != VR_RANGE)
+    return false;
+
+  /* Return true (to set SRP_SIGNED_AND_UNSIGNED to SUBREG) if MSB of the smaller
+     mode is not set (i.e. MSB of ssa is not set).  */
+  if (!wi::neg_p (min, SIGNED) && !wi::neg_p(max, SIGNED))
+    return true;
+  else
+    return false;
+
+}
 
 /* Return TRUE if expression STMT is suitable for replacement.  
    Never consider memory loads as replaceable, because those don't ever lead 
@@ -9527,7 +9557,10 @@ expand_expr_real_1 (tree exp, rtx target, enum machine_mode tmode,
 
 	  temp = gen_lowpart_SUBREG (mode, decl_rtl);
 	  SUBREG_PROMOTED_VAR_P (temp) = 1;
-	  SUBREG_PROMOTED_SET (temp, unsignedp);
+	  if (promoted_for_signed_and_unsigned_p (ssa_name, mode))
+	    SUBREG_PROMOTED_SET (temp, SRP_SIGNED_AND_UNSIGNED);
+	  else
+	    SUBREG_PROMOTED_SET (temp, unsignedp);
 	  return temp;
 	}
 
diff --git a/gcc/expr.h b/gcc/expr.h
index 6a1d3ab..a429509 100644
--- a/gcc/expr.h
+++ b/gcc/expr.h
@@ -440,6 +440,7 @@ extern rtx expand_expr_real_1 (tree, rtx, enum machine_mode,
 			       enum expand_modifier, rtx *, bool);
 extern rtx expand_expr_real_2 (sepops, rtx, enum machine_mode,
 			       enum expand_modifier);
+extern bool promoted_for_signed_and_unsigned_p (tree, enum machine_mode);
 
 /* Generate code for computing expression EXP.
    An rtx for the computed value is returned.  The value is never null.
diff --git a/gcc/testsuite/gcc.dg/zero_sign_ext_test.c b/gcc/testsuite/gcc.dg/zero_sign_ext_test.c
index e69de29..6a52678 100644
--- a/gcc/testsuite/gcc.dg/zero_sign_ext_test.c
+++ b/gcc/testsuite/gcc.dg/zero_sign_ext_test.c
@@ -0,0 +1,136 @@
+extern void abort (void);
+
+/* { dg-options "-O2" } */
+/* { dg-do run } */
+
+#define TYPE_MAX(type, sign)	\
+  ((!sign) ? ((1 << (sizeof (type) * 8 - 1)) - 1) :	\
+   ((1 << (sizeof (type) * 8)) - 1))
+#define TYPE_MIN(type, sign)	\
+  ((!sign) ? -(1 << (sizeof (type) * 8 - 1)) : 0)
+
+#define TEST_FN(NAME, ARG_TYPE, RET_TYPE, CAST_TYPE, VAL, VR_MIN, VR_MAX)\
+  __attribute__((noinline, noclone)) RET_TYPE				\
+      NAME (ARG_TYPE arg){						\
+      RET_TYPE ret = VAL;						\
+      if (arg + 1 < VR_MIN || arg + 1 > VR_MAX) return ret;		\
+      /* Value Range of arg at this point will be  [VR_min, VR_max].  */\
+      arg = arg + VAL;							\
+      ret = (CAST_TYPE)arg;						\
+      return arg;							\
+  }
+
+/* Signed to signed conversion with value in-range.  */
+TEST_FN (foo1, short, short, char, 1, TYPE_MIN (char, 0), TYPE_MAX (char, 0));
+TEST_FN (foo2, short, short, char, 1, TYPE_MIN (char, 0) + 1,\
+	TYPE_MAX (char, 0) - 1);
+
+/* Signed to signed conversion with value not in-range.  */
+TEST_FN (foo3, short, short, char, -1, TYPE_MIN (short, 0) + 1,  100);
+TEST_FN (foo4, short, short, char, 1, 12, TYPE_MAX (short, 0) + 1);
+
+/* Unsigned to unsigned conversion with value in-range.  */
+TEST_FN (foo5, unsigned short, unsigned short, unsigned char, 1,\
+	TYPE_MIN (char, 1) + 1, TYPE_MAX (char, 1) - 1);
+TEST_FN (foo6, unsigned short, unsigned short, unsigned char, 1,\
+	TYPE_MIN (char, 1), TYPE_MAX (char, 1));
+
+/* Unsigned to unsigned conversion with value not in-range.  */
+TEST_FN (foo7, unsigned short, unsigned short, unsigned char, 1,\
+	TYPE_MIN (short, 1) + 1, TYPE_MAX (short, 1) - 1);
+TEST_FN (foo8, unsigned short, unsigned short, unsigned char, 1,\
+	TYPE_MIN (short, 1), TYPE_MAX (short, 1));
+
+/* Signed to unsigned conversion with value range positive.  */
+TEST_FN (foo9, short, short, unsigned char, -1, 1,\
+	TYPE_MAX (char, 1) - 1);
+TEST_FN (foo10, short, short, unsigned char, 1, 0,\
+	TYPE_MAX (char, 1));
+
+/* Signed to unsigned conversion with value range negative.  */
+TEST_FN (foo11, short, short, unsigned char, 1,\
+	TYPE_MIN (char, 0) + 1, TYPE_MAX (char, 0) - 1);
+TEST_FN (foo12, short, short, unsigned char, 1,\
+	TYPE_MIN (char, 0), TYPE_MAX (char, 0));
+
+/* Unsigned to Signed conversion with value range in signed equiv range.  */
+TEST_FN (foo13, unsigned short, unsigned short, char, 1,\
+	TYPE_MIN (char, 1) + 1, TYPE_MAX (char, 0) - 1);
+TEST_FN (foo14, unsigned short, unsigned short, char, 1,\
+	TYPE_MIN (char, 1), TYPE_MAX (char, 0));
+
+/* Unsigned to Signed conversion with value range not-in signed range.  */
+TEST_FN (foo15, unsigned short, unsigned short, char, 1,\
+	TYPE_MIN (char, 1) + 1, TYPE_MAX (char, 1) - 1);
+TEST_FN (foo16, unsigned short, unsigned short, char, 1,\
+	TYPE_MIN (char, 1), TYPE_MAX (char, 1));
+
+int main ()
+{
+  /* Signed to signed conversion with value in-range.  */
+  /* arg + 1.  */
+  if (foo1 (-32) != -31)
+    abort ();
+  /* arg + 1.  */
+  if (foo2 (32) != 33)
+    abort ();
+
+  /* Signed to signed conversion with value not in-range.  */
+  /* arg - 1.  */
+  if (foo3 (-512) != -513)
+    abort ();
+  /* arg + 1.  */
+  if (foo4 (512) != 513)
+    abort ();
+
+  /* Unsigned to unsigned conversion with value in-range.  */
+  /* arg + 1.  */
+  if (foo5 (64) != 65)
+    abort ();
+  /* arg + 1.  */
+  if (foo6 (64) != 65)
+    abort ();
+
+  /* Unsigned to unsigned conversion with value not in-range.  */
+  /* arg + 1.  */
+  if (foo7 (512) != 513)
+    abort ();
+  /* arg + 1.  */
+  if (foo8 (512) != 513)
+    abort ();
+
+  /* Signed to unsigned conversion with value range positive.  */
+  /* arg - 1.  */
+  if (foo9 (2) != 1)
+    abort ();
+  /* arg + 1.  */
+  if (foo10 (2) != 3)
+    abort ();
+
+  /* Signed to unsigned conversion with value range negative.  */
+  /* arg + 1.  */
+  if (foo11 (-125) != -124)
+    abort ();
+  /* arg + 1.  */
+  if (foo12 (-125) != -124)
+    abort ();
+
+  /* Unsigned to Signed conversion with value range in signed equiv range.  */
+  /* arg + 1.  */
+  if (foo13 (125) != 126)
+    abort ();
+  /* arg + 1.  */
+  if (foo14 (125) != 126)
+    abort ();
+
+  /* Unsigned to Signed conversion with value range not-in signed range.  */
+  /* arg + 1.  */
+  if (foo15 (250) != 251)
+    abort ();
+  /* arg + 1.  */
+  if (foo16 (250) != 251)
+    abort ();
+
+  return 0;
+}
+