Fold truncations of left shifts in match.pd

Whilst investigating PR 55278, I noticed that the tree-ssa optimizers
aren't eliminating the promotions of shifts to "int" as inserted by the
c-family front-ends, instead leaving this simplification to be left to
the RTL optimizers.  This patch allows match.pd to do this itself earlier,
narrowing (T)(X << C) to (T)X << C when the constant C is known to be
valid for the (narrower) type T.

Hence for this simple test case:
short foo(short x) { return x << 5; }

the .optimized dump currently looks like:

short int foo (short int x)
{
  int _1;
  int _2;
  short int _4;

  <bb 2> [local count: 1073741824]:
  _1 = (int) x_3(D);
  _2 = _1 << 5;
  _4 = (short int) _2;
  return _4;
}

but with this patch, now becomes:

short int foo (short int x)
{
  short int _2;

  <bb 2> [local count: 1073741824]:
  _2 = x_1(D) << 5;
  return _2;
}

This is always reasonable as RTL expansion knows how to use
widening optabs if it makes sense at the RTL level to perform
this shift in a wider mode.

Of course, there's often a catch.  The above simplification not only
reduces the number of statements in gimple, but also allows further
optimizations, for example including the perception of rotate idioms
and bswap16.  Alas, optimizing things earlier than anticipated
requires several testsuite changes [though all these tests have
been confirmed to generate identical assembly code on x86_64].
The only significant change is that the vectorization pass wouldn't
previously lower rotations of signed integer types.  Hence this
patch includes a refinement to tree-vect-patterns to allow signed
types, by using the equivalent unsigned shifts.

2022-06-15  Roger Sayle  <roger@nextmovesoftware.com>
	    Richard Biener  <rguenther@suse.de>

gcc/ChangeLog
	* match.pd (convert (lshift @1 INTEGER_CST@2)): Narrow integer
	left shifts by a constant when the result is truncated, and the
	shift constant is well-defined.
	* tree-vect-patterns.cc (vect_recog_rotate_pattern): Add
	support for rotations of signed integer types, by lowering
	using unsigned vector shifts.

gcc/testsuite/ChangeLog
	* gcc.dg/fold-convlshift-4.c: New test case.
	* gcc.dg/optimize-bswaphi-1.c: Update found bswap count.
	* gcc.dg/tree-ssa/pr61839_3.c: Shift is now optimized before VRP.
	* gcc.dg/vect/vect-over-widen-1-big-array.c: Remove obsolete tests.
	* gcc.dg/vect/vect-over-widen-1.c: Likewise.
	* gcc.dg/vect/vect-over-widen-3-big-array.c: Likewise.
	* gcc.dg/vect/vect-over-widen-3.c: Likewise.
	* gcc.dg/vect/vect-over-widen-4-big-array.c: Likewise.
	* gcc.dg/vect/vect-over-widen-4.c: Likewise.

11 files changed, 49 insertions, 44 deletions

diff --git a/gcc/match.pd b/gcc/match.pd
index 776c9c64..d4058d6 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -3621,17 +3621,18 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
     (if (integer_zerop (@2) || integer_all_onesp (@2))
      (cmp @0 @2)))))
 
-/* Both signed and unsigned lshift produce the same result, so use
-   the form that minimizes the number of conversions.  Postpone this
-   transformation until after shifts by zero have been folded.  */
+/* Narrow a lshift by constant.  */
 (simplify
- (convert (lshift:s@0 (convert:s@1 @2) INTEGER_CST@3))
+ (convert (lshift:s@0 @1 INTEGER_CST@2))
  (if (INTEGRAL_TYPE_P (type)
-      && tree_nop_conversion_p (type, TREE_TYPE (@0))
-      && INTEGRAL_TYPE_P (TREE_TYPE (@2))
-      && TYPE_PRECISION (TREE_TYPE (@2)) <= TYPE_PRECISION (type)
-      && !integer_zerop (@3))
-  (lshift (convert @2) @3)))
+      && INTEGRAL_TYPE_P (TREE_TYPE (@0))
+      && !integer_zerop (@2)
+      && TYPE_PRECISION (type) <= TYPE_PRECISION (TREE_TYPE (@0)))
+  (if (TYPE_PRECISION (type) == TYPE_PRECISION (TREE_TYPE (@0))
+       || wi::ltu_p (wi::to_wide (@2), TYPE_PRECISION (type)))
+   (lshift (convert @1) @2)
+   (if (wi::ltu_p (wi::to_wide (@2), TYPE_PRECISION (TREE_TYPE (@0))))
+    { build_zero_cst (type); }))))
 
 /* Simplifications of conversions.  */
 
diff --git a/gcc/testsuite/gcc.dg/fold-convlshift-4.c b/gcc/testsuite/gcc.dg/fold-convlshift-4.c
new file mode 100644
index 0000000..001627f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/fold-convlshift-4.c
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+short foo(short x)
+{
+  return x << 5;
+}
+
+/* { dg-final { scan-tree-dump-not "\\(int\\)" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "\\(short int\\)" "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/optimize-bswaphi-1.c b/gcc/testsuite/gcc.dg/optimize-bswaphi-1.c
index d045da9..a5d8bfd 100644
--- a/gcc/testsuite/gcc.dg/optimize-bswaphi-1.c
+++ b/gcc/testsuite/gcc.dg/optimize-bswaphi-1.c
@@ -68,4 +68,4 @@ get_unaligned_16_be (unsigned char *p)
 
 
 /* { dg-final { scan-tree-dump-times "16 bit load in target endianness found at" 4 "bswap" } } */
-/* { dg-final { scan-tree-dump-times "16 bit bswap implementation found at" 5 "bswap" } } */
+/* { dg-final { scan-tree-dump-times "16 bit bswap implementation found at" 4 "bswap" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr61839_3.c b/gcc/testsuite/gcc.dg/tree-ssa/pr61839_3.c
index bc2126f..38cf792 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/pr61839_3.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr61839_3.c
@@ -1,6 +1,6 @@
 /* PR tree-optimization/61839.  */
 /* { dg-do run } */
-/* { dg-options "-O2 -fdump-tree-vrp -fdump-tree-optimized -fdisable-tree-ethread -fdisable-tree-threadfull1" } */
+/* { dg-options "-O2 -fdump-tree-optimized -fdisable-tree-ethread -fdisable-tree-threadfull1" } */
 
 __attribute__ ((noinline))
 int foo (int a, unsigned b)
@@ -21,6 +21,4 @@ int main ()
   foo (-1, b);
 }
 
-/* Scan for c [12, 13] << 8 in function foo.  */
-/* { dg-final { scan-tree-dump-times "3072 : 3328" 1  "vrp1" } } */
 /* { dg-final { scan-tree-dump-times "3072" 0  "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-over-widen-1-big-array.c b/gcc/testsuite/gcc.dg/vect/vect-over-widen-1-big-array.c
index 9e5f464..9a5141ee 100644
--- a/gcc/testsuite/gcc.dg/vect/vect-over-widen-1-big-array.c
+++ b/gcc/testsuite/gcc.dg/vect/vect-over-widen-1-big-array.c
@@ -58,9 +58,7 @@ int main (void)
 }
 
 /* { dg-final { scan-tree-dump-times "vect_recog_widen_shift_pattern: detected" 2 "vect" { target vect_widen_shift } } } */
-/* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* << 3} "vect" } } */
 /* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* >> 3} "vect" } } */
-/* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* << 8} "vect" } } */
 /* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* >> 5} "vect" } } */
 /* { dg-final { scan-tree-dump-times "vectorized 1 loops" 1 "vect" } } */
 
diff --git a/gcc/testsuite/gcc.dg/vect/vect-over-widen-1.c b/gcc/testsuite/gcc.dg/vect/vect-over-widen-1.c
index c2d0797..f2d284c 100644
--- a/gcc/testsuite/gcc.dg/vect/vect-over-widen-1.c
+++ b/gcc/testsuite/gcc.dg/vect/vect-over-widen-1.c
@@ -62,9 +62,7 @@ int main (void)
 }
 
 /* { dg-final { scan-tree-dump-times "vect_recog_widen_shift_pattern: detected" 2 "vect" { target vect_widen_shift } } } */
-/* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* << 3} "vect" } } */
 /* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* >> 3} "vect" } } */
-/* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* << 8} "vect" } } */
 /* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* >> 5} "vect" } } */
 /* { dg-final { scan-tree-dump-times "vectorized 1 loops" 1 "vect" } } */
 
diff --git a/gcc/testsuite/gcc.dg/vect/vect-over-widen-3-big-array.c b/gcc/testsuite/gcc.dg/vect/vect-over-widen-3-big-array.c
index 37da7c9..6f89aac 100644
--- a/gcc/testsuite/gcc.dg/vect/vect-over-widen-3-big-array.c
+++ b/gcc/testsuite/gcc.dg/vect/vect-over-widen-3-big-array.c
@@ -59,9 +59,7 @@ int main (void)
   return 0;
 }
 
-/* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* << 3} "vect" } } */
 /* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* >> 3} "vect" } } */
 /* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* >> 8} "vect" } } */
-/* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* << 9} "vect" } } */
 /* { dg-final { scan-tree-dump-times "vectorized 1 loops" 1 "vect" } } */
 
diff --git a/gcc/testsuite/gcc.dg/vect/vect-over-widen-3.c b/gcc/testsuite/gcc.dg/vect/vect-over-widen-3.c
index 4138480..a1e1182 100644
--- a/gcc/testsuite/gcc.dg/vect/vect-over-widen-3.c
+++ b/gcc/testsuite/gcc.dg/vect/vect-over-widen-3.c
@@ -57,9 +57,7 @@ int main (void)
   return 0;
 }
 
-/* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* << 3} "vect" } } */
 /* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* >> 3} "vect" } } */
 /* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* >> 8} "vect" } } */
-/* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* << 9} "vect" } } */
 /* { dg-final { scan-tree-dump-times "vectorized 1 loops" 1 "vect" } } */
 
diff --git a/gcc/testsuite/gcc.dg/vect/vect-over-widen-4-big-array.c b/gcc/testsuite/gcc.dg/vect/vect-over-widen-4-big-array.c
index 514337c..03a6e67 100644
--- a/gcc/testsuite/gcc.dg/vect/vect-over-widen-4-big-array.c
+++ b/gcc/testsuite/gcc.dg/vect/vect-over-widen-4-big-array.c
@@ -62,9 +62,7 @@ int main (void)
 }
 
 /* { dg-final { scan-tree-dump-times "vect_recog_widen_shift_pattern: detected" 2 "vect" { target vect_widen_shift } } } */
-/* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* << 3} "vect" } } */
 /* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* >> 3} "vect" } } */
-/* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* << 8} "vect" } } */
 /* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* >> 5} "vect" } } */
 /* { dg-final { scan-tree-dump-times "vectorized 1 loops" 1 "vect" } } */
 
diff --git a/gcc/testsuite/gcc.dg/vect/vect-over-widen-4.c b/gcc/testsuite/gcc.dg/vect/vect-over-widen-4.c
index 3d536d5..0ef377f 100644
--- a/gcc/testsuite/gcc.dg/vect/vect-over-widen-4.c
+++ b/gcc/testsuite/gcc.dg/vect/vect-over-widen-4.c
@@ -66,9 +66,7 @@ int main (void)
 }
 
 /* { dg-final { scan-tree-dump-times "vect_recog_widen_shift_pattern: detected" 2 "vect" { target vect_widen_shift } } } */
-/* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* << 3} "vect" } } */
 /* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* >> 3} "vect" } } */
-/* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* << 8} "vect" } } */
 /* { dg-final { scan-tree-dump {vect_recog_over_widening_pattern: detected:[^\n]* >> 5} "vect" } } */
 /* { dg-final { scan-tree-dump-times "vectorized 1 loops" 1 "vect" } } */
 
diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
index 0fad4db..8f62486 100644
--- a/gcc/tree-vect-patterns.cc
+++ b/gcc/tree-vect-patterns.cc
@@ -2614,8 +2614,7 @@ vect_recog_rotate_pattern (vec_info *vinfo,
 	  || TYPE_PRECISION (TREE_TYPE (lhs)) != 16
 	  || TYPE_PRECISION (type) <= 16
 	  || TREE_CODE (oprnd0) != SSA_NAME
-	  || BITS_PER_UNIT != 8
-	  || !TYPE_UNSIGNED (TREE_TYPE (lhs)))
+	  || BITS_PER_UNIT != 8)
 	return NULL;
 
       stmt_vec_info def_stmt_info;
@@ -2688,8 +2687,7 @@ vect_recog_rotate_pattern (vec_info *vinfo,
 
   if (TREE_CODE (oprnd0) != SSA_NAME
       || TYPE_PRECISION (TREE_TYPE (lhs)) != TYPE_PRECISION (type)
-      || !INTEGRAL_TYPE_P (type)
-      || !TYPE_UNSIGNED (type))
+      || !INTEGRAL_TYPE_P (type))
     return NULL;
 
   stmt_vec_info def_stmt_info;
@@ -2745,31 +2743,36 @@ vect_recog_rotate_pattern (vec_info *vinfo,
 	goto use_rotate;
     }
 
+  tree utype = unsigned_type_for (type);
+  tree uvectype = get_vectype_for_scalar_type (vinfo, utype);
+  if (!uvectype)
+    return NULL;
+
   /* If vector/vector or vector/scalar shifts aren't supported by the target,
      don't do anything here either.  */
-  optab1 = optab_for_tree_code (LSHIFT_EXPR, vectype, optab_vector);
-  optab2 = optab_for_tree_code (RSHIFT_EXPR, vectype, optab_vector);
+  optab1 = optab_for_tree_code (LSHIFT_EXPR, uvectype, optab_vector);
+  optab2 = optab_for_tree_code (RSHIFT_EXPR, uvectype, optab_vector);
   if (!optab1
-      || optab_handler (optab1, TYPE_MODE (vectype)) == CODE_FOR_nothing
+      || optab_handler (optab1, TYPE_MODE (uvectype)) == CODE_FOR_nothing
       || !optab2
-      || optab_handler (optab2, TYPE_MODE (vectype)) == CODE_FOR_nothing)
+      || optab_handler (optab2, TYPE_MODE (uvectype)) == CODE_FOR_nothing)
     {
       if (! is_a <bb_vec_info> (vinfo) && dt == vect_internal_def)
 	return NULL;
-      optab1 = optab_for_tree_code (LSHIFT_EXPR, vectype, optab_scalar);
-      optab2 = optab_for_tree_code (RSHIFT_EXPR, vectype, optab_scalar);
+      optab1 = optab_for_tree_code (LSHIFT_EXPR, uvectype, optab_scalar);
+      optab2 = optab_for_tree_code (RSHIFT_EXPR, uvectype, optab_scalar);
       if (!optab1
-	  || optab_handler (optab1, TYPE_MODE (vectype)) == CODE_FOR_nothing
+	  || optab_handler (optab1, TYPE_MODE (uvectype)) == CODE_FOR_nothing
 	  || !optab2
-	  || optab_handler (optab2, TYPE_MODE (vectype)) == CODE_FOR_nothing)
+	  || optab_handler (optab2, TYPE_MODE (uvectype)) == CODE_FOR_nothing)
 	return NULL;
     }
 
   *type_out = vectype;
 
-  if (bswap16_p && !useless_type_conversion_p (type, TREE_TYPE (oprnd0)))
+  if (!useless_type_conversion_p (utype, TREE_TYPE (oprnd0)))
     {
-      def = vect_recog_temp_ssa_var (type, NULL);
+      def = vect_recog_temp_ssa_var (utype, NULL);
       def_stmt = gimple_build_assign (def, NOP_EXPR, oprnd0);
       append_pattern_def_seq (vinfo, stmt_vinfo, def_stmt);
       oprnd0 = def;
@@ -2779,7 +2782,7 @@ vect_recog_rotate_pattern (vec_info *vinfo,
     ext_def = vect_get_external_def_edge (vinfo, oprnd1);
 
   def = NULL_TREE;
-  scalar_int_mode mode = SCALAR_INT_TYPE_MODE (type);
+  scalar_int_mode mode = SCALAR_INT_TYPE_MODE (utype);
   if (dt != vect_internal_def || TYPE_MODE (TREE_TYPE (oprnd1)) == mode)
     def = oprnd1;
   else if (def_stmt && gimple_assign_cast_p (def_stmt))
@@ -2793,7 +2796,7 @@ vect_recog_rotate_pattern (vec_info *vinfo,
 
   if (def == NULL_TREE)
     {
-      def = vect_recog_temp_ssa_var (type, NULL);
+      def = vect_recog_temp_ssa_var (utype, NULL);
       def_stmt = gimple_build_assign (def, NOP_EXPR, oprnd1);
       append_pattern_def_seq (vinfo, stmt_vinfo, def_stmt);
     }
@@ -2839,13 +2842,13 @@ vect_recog_rotate_pattern (vec_info *vinfo,
 	append_pattern_def_seq (vinfo, stmt_vinfo, def_stmt, vecstype);
     }
 
-  var1 = vect_recog_temp_ssa_var (type, NULL);
+  var1 = vect_recog_temp_ssa_var (utype, NULL);
   def_stmt = gimple_build_assign (var1, rhs_code == LROTATE_EXPR
 					? LSHIFT_EXPR : RSHIFT_EXPR,
 				  oprnd0, def);
   append_pattern_def_seq (vinfo, stmt_vinfo, def_stmt);
 
-  var2 = vect_recog_temp_ssa_var (type, NULL);
+  var2 = vect_recog_temp_ssa_var (utype, NULL);
   def_stmt = gimple_build_assign (var2, rhs_code == LROTATE_EXPR
 					? RSHIFT_EXPR : LSHIFT_EXPR,
 				  oprnd0, def2);
@@ -2855,9 +2858,15 @@ vect_recog_rotate_pattern (vec_info *vinfo,
   vect_pattern_detected ("vect_recog_rotate_pattern", last_stmt);
 
   /* Pattern supported.  Create a stmt to be used to replace the pattern.  */
-  var = vect_recog_temp_ssa_var (type, NULL);
+  var = vect_recog_temp_ssa_var (utype, NULL);
   pattern_stmt = gimple_build_assign (var, BIT_IOR_EXPR, var1, var2);
 
+  if (!useless_type_conversion_p (type, utype))
+    {
+      append_pattern_def_seq (vinfo, stmt_vinfo, pattern_stmt);
+      tree result = vect_recog_temp_ssa_var (type, NULL);
+      pattern_stmt = gimple_build_assign (result, NOP_EXPR, var);
+    }
   return pattern_stmt;
 }