[gcc r12-2657] Optimize x ? bswap(x) : 0 in tree-ssa-phiopt

[gcc r12-2657] Optimize x ? bswap(x) : 0 in tree-ssa-phiopt

[Roger Sayle]

https://gcc.gnu.org/g:f9fcf754825a1e01033336f84c18690aaa971a6f

commit r12-2657-gf9fcf754825a1e01033336f84c18690aaa971a6f
Author: Roger Sayle <roger@nextmovesoftware.com>
Date:   Mon Aug 2 13:27:53 2021 +0100

    Optimize x ? bswap(x) : 0 in tree-ssa-phiopt
    
    Many thanks again to Jakub Jelinek for a speedy fix for PR 101642.
    Interestingly, that test case "bswap16(x) ? : x" also reveals a
    missed optimization opportunity.  The resulting "x ? bswap(x) : 0"
    can be further simplified to just bswap(x).
    
    Conveniently, tree-ssa-phiopt.c already recognizes/optimizes the
    related "x ? popcount(x) : 0", so this patch simply makes that
    transformation make general, additionally handling bswap, parity,
    ffs and clrsb.  All of the required infrastructure is already
    present thanks to Jakub previously adding support for clz/ctz.
    To reflect this generalization, the name of the function is changed
    from cond_removal_in_popcount_clz_ctz_pattern to the hopefully
    equally descriptive cond_removal_in_builtin_zero_pattern.
    
    2021-08-02  Roger Sayle  <roger@nextmovesoftware.com>
    
    gcc/ChangeLog
            * tree-ssa-phiopt.c (cond_removal_in_builtin_zero_pattern):
            Renamed from cond_removal_in_popcount_clz_ctz_pattern.
            Add support for BSWAP, FFS, PARITY and CLRSB builtins.
            (tree_ssa_phiop_worker): Update call to function above.
    
    gcc/testsuite/ChangeLog
            * gcc.dg/tree-ssa/phi-opt-25.c: New test case.

Diff:
---
 gcc/testsuite/gcc.dg/tree-ssa/phi-opt-25.c | 83 ++++++++++++++++++++++++++++++
 gcc/tree-ssa-phiopt.c                      | 37 +++++++++----
 2 files changed, 109 insertions(+), 11 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/phi-opt-25.c b/gcc/testsuite/gcc.dg/tree-ssa/phi-opt-25.c
new file mode 100644
index 00000000000..c52c92e1d45
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/phi-opt-25.c
@@ -0,0 +1,83 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+unsigned short test_bswap16(unsigned short x)
+{
+  return x ? __builtin_bswap16(x) : 0;
+}
+
+unsigned int test_bswap32(unsigned int x)
+{
+  return x ? __builtin_bswap32(x) : 0;
+}
+
+unsigned long long test_bswap64(unsigned long long x)
+{
+  return x ? __builtin_bswap64(x) : 0;
+}
+
+int test_clrsb(int x)
+{
+  return x ? __builtin_clrsb(x) : (__SIZEOF_INT__*8-1);
+}
+
+int test_clrsbl(long x)
+{
+  return x ? __builtin_clrsbl(x) : (__SIZEOF_LONG__*8-1);
+}
+
+int test_clrsbll(long long x)
+{
+  return x ? __builtin_clrsbll(x) : (__SIZEOF_LONG_LONG__*8-1);
+}
+
+#if 0
+/* BUILT_IN_FFS is transformed by match.pd */
+int test_ffs(unsigned int x)
+{
+  return x ? __builtin_ffs(x) : 0;
+}
+
+int test_ffsl(unsigned long x)
+{
+  return x ? __builtin_ffsl(x) : 0;
+}
+
+int test_ffsll(unsigned long long x)
+{
+  return x ? __builtin_ffsll(x) : 0;
+}
+#endif
+
+int test_parity(int x)
+{
+  return x ? __builtin_parity(x) : 0;
+}
+
+int test_parityl(long x)
+{
+  return x ? __builtin_parityl(x) : 0;
+}
+
+int test_parityll(long long x)
+{
+  return x ? __builtin_parityll(x) : 0;
+}
+
+int test_popcount(int x)
+{
+  return x ? __builtin_popcount(x) : 0;
+}
+
+int test_popcountl(long x)
+{
+  return x ? __builtin_popcountl(x) : 0;
+}
+
+int test_popcountll(long long x)
+{
+  return x ? __builtin_popcountll(x) : 0;
+}
+
+/* { dg-final { scan-tree-dump-not "goto" "optimized" } } */
+
diff --git a/gcc/tree-ssa-phiopt.c b/gcc/tree-ssa-phiopt.c
index c6adbbd28a0..66af902e37e 100644
--- a/gcc/tree-ssa-phiopt.c
+++ b/gcc/tree-ssa-phiopt.c
@@ -66,9 +66,9 @@ static bool minmax_replacement (basic_block, basic_block,
 				edge, edge, gphi *, tree, tree);
 static bool spaceship_replacement (basic_block, basic_block,
 				   edge, edge, gphi *, tree, tree);
-static bool cond_removal_in_popcount_clz_ctz_pattern (basic_block, basic_block,
-						      edge, edge, gphi *,
-						      tree, tree);
+static bool cond_removal_in_builtin_zero_pattern (basic_block, basic_block,
+						  edge, edge, gphi *,
+						  tree, tree);
 static bool cond_store_replacement (basic_block, basic_block, edge, edge,
 				    hash_set<tree> *);
 static bool cond_if_else_store_replacement (basic_block, basic_block, basic_block);
@@ -350,9 +350,8 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool do_hoist_loads, bool early_p)
 					       early_p))
 	    cfgchanged = true;
 	  else if (!early_p
-		   && cond_removal_in_popcount_clz_ctz_pattern (bb, bb1, e1,
-								e2, phi, arg0,
-								arg1))
+		   && cond_removal_in_builtin_zero_pattern (bb, bb1, e1, e2,
+							    phi, arg0, arg1))
 	    cfgchanged = true;
 	  else if (minmax_replacement (bb, bb1, e1, e2, phi, arg0, arg1))
 	    cfgchanged = true;
@@ -2466,7 +2465,8 @@ spaceship_replacement (basic_block cond_bb, basic_block middle_bb,
   return true;
 }
 
-/* Convert
+/* Optimize x ? __builtin_fun (x) : C, where C is __builtin_fun (0).
+   Convert
 
    <bb 2>
    if (b_4(D) != 0)
@@ -2498,10 +2498,10 @@ spaceship_replacement (basic_block cond_bb, basic_block middle_bb,
    instead of 0 above it uses the value from that macro.  */
 
 static bool
-cond_removal_in_popcount_clz_ctz_pattern (basic_block cond_bb,
-					  basic_block middle_bb,
-					  edge e1, edge e2, gphi *phi,
-					  tree arg0, tree arg1)
+cond_removal_in_builtin_zero_pattern (basic_block cond_bb,
+				      basic_block middle_bb,
+				      edge e1, edge e2, gphi *phi,
+				      tree arg0, tree arg1)
 {
   gimple *cond;
   gimple_stmt_iterator gsi, gsi_from;
@@ -2549,6 +2549,12 @@ cond_removal_in_popcount_clz_ctz_pattern (basic_block cond_bb,
   int val = 0;
   switch (cfn)
     {
+    case CFN_BUILT_IN_BSWAP16:
+    case CFN_BUILT_IN_BSWAP32:
+    case CFN_BUILT_IN_BSWAP64:
+    case CFN_BUILT_IN_BSWAP128:
+    CASE_CFN_FFS:
+    CASE_CFN_PARITY:
     CASE_CFN_POPCOUNT:
       break;
     CASE_CFN_CLZ:
@@ -2577,6 +2583,15 @@ cond_removal_in_popcount_clz_ctz_pattern (basic_block cond_bb,
 	    }
 	}
       return false;
+    case BUILT_IN_CLRSB:
+      val = TYPE_PRECISION (integer_type_node) - 1;
+      break;
+    case BUILT_IN_CLRSBL:
+      val = TYPE_PRECISION (long_integer_type_node) - 1;
+      break;
+    case BUILT_IN_CLRSBLL:
+      val = TYPE_PRECISION (long_long_integer_type_node) - 1;
+      break;
     default:
       return false;
     }