[PATCH] match.pd: rewrite select to branchless expression

[Michael Collison <collison@rivosinc.com>]

This patches transforms (cond (and (x , 0x1) == 0), y, (z op y)) into 
(-(and (x , 0x1)) & z ) op y, where op is a '^' or a '|'. It also 
transforms (cond (and (x , 0x1) != 0), (z op y), y ) into (-(and (x , 
0x1)) & z ) op y.

Matching this patterns allows GCC to generate branchless code for one of 
the functions in coremark.

Bootstrapped and tested on x86 and RISC-V. Okay?

Michael.

2022-11-08  Michael Collison  <collison@rivosinc.com>

     * match.pd ((cond (and (x , 0x1) == 0), y, (z op y) )
     -> (-(and (x , 0x1)) & z ) op y)

2022-11-08  Michael Collison  <collison@rivosinc.com>

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

---
  gcc/match.pd                                  | 22 ++++++++++++++++
  .../gcc.dg/tree-ssa/branchless-cond.c         | 26 +++++++++++++++++++
  2 files changed, 48 insertions(+)
  create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/branchless-cond.c

diff --git a/gcc/match.pd b/gcc/match.pd
index 194ba8f5188..722f517ac6d 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -3486,6 +3486,28 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
    (cond (le @0 integer_zerop@1) (negate@2 @0) integer_zerop@1)
    (max @2 @1))

+/* (cond (and (x , 0x1) == 0), y, (z ^ y) ) -> (-(and (x , 0x1)) & z ) 
^ y */
+(for op (bit_xor bit_ior)
+ (simplify
+  (cond (eq (bit_and @0 integer_onep@1)
+            integer_zerop)
+        @2
+        (op:c @3 @2))
+  (if (INTEGRAL_TYPE_P (type)
+       && (INTEGRAL_TYPE_P (TREE_TYPE (@0))))
+       (op (bit_and (negate (convert:type (bit_and @0 @1))) @3) @2))))
+
+/* (cond (and (x , 0x1) != 0), (z ^ y), y ) -> (-(and (x , 0x1)) & z ) 
^ y */
+(for op (bit_xor bit_ior)
+ (simplify
+  (cond (ne (bit_and @0 integer_onep@1)
+            integer_zerop)
+    (op:c @3 @2)
+        @2)
+  (if (INTEGRAL_TYPE_P (type)
+       && (INTEGRAL_TYPE_P (TREE_TYPE (@0))))
+       (op (bit_and (negate (convert:type (bit_and @0 @1))) @3) @2))))
+
  /* Simplifications of shift and rotates.  */

  (for rotate (lrotate rrotate)
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/branchless-cond.c 
b/gcc/testsuite/gcc.dg/tree-ssa/branchless-cond.c
new file mode 100644
index 00000000000..68087ae6568
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/branchless-cond.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+int f1(unsigned int x, unsigned int y, unsigned int z)
+{
+  return ((x & 1) == 0) ? y : z ^ y;
+}
+
+int f2(unsigned int x, unsigned int y, unsigned int z)
+{
+  return ((x & 1) != 0) ? z ^ y : y;
+}
+
+int f3(unsigned int x, unsigned int y, unsigned int z)
+{
+  return ((x & 1) == 0) ? y : z | y;
+}
+
+int f4(unsigned int x, unsigned int y, unsigned int z)
+{
+  return ((x & 1) != 0) ? z | y : y;
+}
+
+/* { dg-final { scan-tree-dump-times " -" 4 "optimized" } } */
+/* { dg-final { scan-tree-dump-times " & " 8 "optimized" } } */
+/* { dg-final { scan-tree-dump-not "if" "optimized" } } */
-- 
2.34.1