[to-be-committed] [RISC-V] Improve single inverted bit extraction - v3

[Jeff Law <jlaw@ventanamicro.com>]

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The only change in v2 vs v3 is testsuite adjustments for the updated 
sequences and fixing the name of the second pattern.

--


So this patch fixes a minor code generation inefficiency that (IIRC) the
RAU team discovered a while ago in spec.

If we want the inverted value of a single bit we can use bext to extract
the bit, then seq to invert the value (if viewed as a 0/1 truth value).

The RTL is fairly convoluted, but it's basically a right shift to get
the bit into position, bitwise-not then masking off all but the low bit.
So it's a 3->2 combine, hidden by the fact that and-not is a
define_insn_and_split, so it actually looks like a 2->2 combine.

We've run this through Ventana's internal CI (which includes
zba_zbb_zbs) and I've run it in my own tester (rv64gc, rv32gcv).  I'll
wait for the upstream CI to finish with positive results before pushing.

Jeff


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gcc/
	* config/riscv/bitmanip.md (bextseqzdisi): New patterns.

gcc/testsuite/

	* gcc.target/riscv/zbs-bext-2.c: New test.
	* gcc.target/riscv/zbs-bext.c: Fix one of the possible expectes sequences.
	

diff --git a/gcc/config/riscv/bitmanip.md b/gcc/config/riscv/bitmanip.md
index d76a72d30e0..724511b6df3 100644
--- a/gcc/config/riscv/bitmanip.md
+++ b/gcc/config/riscv/bitmanip.md
@@ -711,6 +711,49 @@ (define_insn "*bext<mode>"
   "bext\t%0,%1,%2"
   [(set_attr "type" "bitmanip")])
 
+;; This is a bext followed by a seqz.  Normally this would be a 3->2 split
+;; But the and-not pattern with a constant operand is a define_insn_and_split,
+;; so this looks like a 2->2 split, which combine rejects.  So implement it
+;; as a define_insn_and_split as well.
+(define_insn_and_split "*bextseqzdisi"
+  [(set (match_operand:DI 0 "register_operand" "=r")
+	(and:DI
+	  (not:DI
+	    (subreg:DI
+	      (lshiftrt:SI
+		(match_operand:SI 1 "register_operand" "r")
+		(match_operand:QI 2 "register_operand" "r")) 0))
+	  (const_int 1)))]
+  "TARGET_64BIT && TARGET_ZBS"
+  "#"
+  "&& 1"
+  [(set (match_dup 0)
+	(zero_extract:DI (match_dup 1)
+			 (const_int 1)
+			 (zero_extend:DI (match_dup 2))))
+   (set (match_dup 0) (eq:DI (match_dup 0) (const_int 0)))]
+  "operands[1] = gen_lowpart (word_mode, operands[1]);"
+  [(set_attr "type" "bitmanip")])
+
+(define_insn_and_split "*bextseqz"
+  [(set (match_operand:X 0 "register_operand" "=r")
+	(and:X
+	  (not:X
+	    (lshiftrt:X
+	      (match_operand:X 1 "register_operand" "r")
+	      (match_operand:QI 2 "register_operand" "r")))
+	  (const_int 1)))]
+  "TARGET_ZBS"
+  "#"
+  "&& 1"
+  [(set (match_dup 0)
+	(zero_extract:X (match_dup 1)
+			(const_int 1)
+			(zero_extend:X (match_dup 2))))
+   (set (match_dup 0) (eq:X (match_dup 0) (const_int 0)))]
+  "operands[1] = gen_lowpart (word_mode, operands[1]);"
+  [(set_attr "type" "bitmanip")])
+
 ;; When performing `(a & (1UL << bitno)) ? 0 : -1` the combiner
 ;; usually has the `bitno` typed as X-mode (i.e. no further
 ;; zero-extension is performed around the bitno).
diff --git a/gcc/testsuite/gcc.target/riscv/zbs-bext-2.c b/gcc/testsuite/gcc.target/riscv/zbs-bext-2.c
new file mode 100644
index 00000000000..79f120b2286
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/zbs-bext-2.c
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gc_zbs -mabi=lp64" } */
+/* { dg-skip-if "" { *-*-* } { "-O0" "-Og" } } */
+
+
+_Bool match(const int ch, int fMap) {
+    return ((fMap & (1<<(ch))) == 0);
+}
+
+_Bool match2(const int ch, int fMap) {
+    return ((fMap & (1UL<<(ch))) == 0);
+}
+
+
+/* { dg-final { scan-assembler-times "bext\t" 2 } } */
+/* { dg-final { scan-assembler-times "seqz\t|xori\t" 2 } } */
+/* { dg-final { scan-assembler-not "sraw\t" } } */
+/* { dg-final { scan-assembler-not "not\t" } } */
+/* { dg-final { scan-assembler-not "andi\t" } } */
diff --git a/gcc/testsuite/gcc.target/riscv/zbs-bext.c b/gcc/testsuite/gcc.target/riscv/zbs-bext.c
index ff75dad6528..0db97f5ab59 100644
--- a/gcc/testsuite/gcc.target/riscv/zbs-bext.c
+++ b/gcc/testsuite/gcc.target/riscv/zbs-bext.c
@@ -38,7 +38,7 @@ long bext64_4(long a, char bitno)
 
 /* { dg-final { scan-assembler-times "bexti\t" 1 } } */
 /* { dg-final { scan-assembler-times "bext\t" 5 } } */
-/* { dg-final { scan-assembler-times "xori\t|snez\t" 1 } } */
+/* { dg-final { scan-assembler-times "xori\t|seqz\t" 1 } } */
 /* { dg-final { scan-assembler-times "addi\t" 1 } } */
 /* { dg-final { scan-assembler-times "neg\t" 1 } } */
 /* { dg-final { scan-assembler-not {\mandi} } } */