match.pd: Simplify BFR of insert when extracting exactly all inserted bits [PR108688]

On Thu, Feb 09, 2023 at 09:16:17AM +0100, Richard Biener via Gcc-patches wrote:
> Hmm.  Can we handle the case of the extraction exactly covering the
> insertion separately then and simplify to plain @1?

I was suggesting that in the PR.  Here it is as an incremental patch
on top of Andrew's patch.

On the newly added testcase the ifcvt-folding difference without/with the
incremental patch is:
--- pr108688.c.171t.ifcvt_      2023-02-09 10:47:30.169916845 +0100
+++ pr108688.c.171t.ifcvt       2023-02-09 10:48:44.942793453 +0100
@@ -25,6 +25,8 @@ Number of blocks in CFG: 11
 Number of blocks to update: 5 ( 45%)

+Applying pattern match.pd:7487, gimple-match.cc:243200
+Applying pattern match.pd:3987, gimple-match.cc:75423
 Matching expression match.pd:1677, gimple-match.cc:209
 Applying pattern match.pd:1733, gimple-match.cc:109481
 Matching expression match.pd:2393, gimple-match.cc:852
@@ -70,7 +72,6 @@ void foo ()
   signed char _29;
   <unnamed-signed:7> _30;
   unsigned int ivtmp_33;
-  <unnamed-signed:7> _ifc__35;
   unsigned char _ifc__37;
   unsigned char _ifc__38;
   unsigned char _ifc__39;
@@ -91,8 +92,7 @@ void foo ()
   _2 = (<unnamed-signed:7>) a.0_1;
   _ifc__38 = u.D.2741;
   _ifc__39 = BIT_INSERT_EXPR <_ifc__38, _2, 0 (7 bits)>;
-  _ifc__35 = BIT_FIELD_REF <_ifc__39, 7, 0>;
-  _4 = (signed char) _ifc__35;
+  _4 = (signed char) _2;
   b.1_5 = b;
   _6 = (signed char) b.1_5;
   _7 = _4 ^ _6;

2023-02-09  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/108688
	* match.pd (bit_field_ref [bit_insert]): Simplify BIT_FIELD_REF
	of BIT_INSERT_EXPR extracting exactly all inserted bits even
	when without mode precision.  Formatting fixes.

	* gcc.c-torture/compile/pr108688-1.c: Add PR number as comment.
	* gcc.dg/pr108688.c: New test.

3 files changed, 23 insertions, 5 deletions

diff --git a/gcc/match.pd b/gcc/match.pd
index 73e5053..821630d 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -7475,13 +7475,16 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
   }
   (switch
    (if ((!INTEGRAL_TYPE_P (TREE_TYPE (@1))
-         || type_has_mode_precision_p (TREE_TYPE (@1)))
-        && wi::leu_p (wi::to_wide (@ipos), wi::to_wide (@rpos))
+	 || type_has_mode_precision_p (TREE_TYPE (@1)))
+	&& wi::leu_p (wi::to_wide (@ipos), wi::to_wide (@rpos))
 	&& wi::leu_p (wi::to_wide (@rpos) + wi::to_wide (@rsize),
 		      wi::to_wide (@ipos) + isize))
     (BIT_FIELD_REF @1 @rsize { wide_int_to_tree (bitsizetype,
-                                                 wi::to_wide (@rpos)
+						 wi::to_wide (@rpos)
 						 - wi::to_wide (@ipos)); }))
+   (if (wi::eq_p (wi::to_wide (@ipos), wi::to_wide (@rpos))
+        && compare_tree_int (@rsize, isize) == 0)
+    (convert @1))
    (if (wi::geu_p (wi::to_wide (@ipos),
 		   wi::to_wide (@rpos) + wi::to_wide (@rsize))
 	|| wi::geu_p (wi::to_wide (@rpos),
diff --git a/gcc/testsuite/gcc.c-torture/compile/pr108688-1.c b/gcc/testsuite/gcc.c-torture/compile/pr108688-1.c
index 43d782d..c300dcb9 100644
--- a/gcc/testsuite/gcc.c-torture/compile/pr108688-1.c
+++ b/gcc/testsuite/gcc.c-torture/compile/pr108688-1.c
@@ -1,4 +1,4 @@
-
+/* PR tree-optimization/108688 */
 
 union U { signed int d : 7; signed int e : 2; } u;
 int a, b;
@@ -12,4 +12,3 @@ foo (void)
       u.e ^= b;
     }
 }
-
diff --git a/gcc/testsuite/gcc.dg/pr108688.c b/gcc/testsuite/gcc.dg/pr108688.c
new file mode 100644
index 0000000..5f76f0b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr108688.c
@@ -0,0 +1,16 @@
+/* PR tree-optimization/108688 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-tree-pre -fno-tree-fre -fno-tree-dominator-opts -fno-tree-loop-im -fno-code-hoisting" } */
+
+union U { signed int d : 7; signed int e : 2; } u;
+int a, b;
+
+void
+foo (void)
+{
+  for (int i = 0; i < 64; i++)
+    {
+      u.d = a;
+      u.d ^= b;
+    }
+}