i386: Optimize double-word negation [PR51954]

Introduce peephole2 pattern to convert from:

   mov %esi, %edx
   negl %eax
   adcl $0, %edx
   negl %edx
 to:
   xorl %edx, %edx
   negl %eax
   sbbl %esi, %edx

This conversion is profitable only when initial move is found.  Otherwise,
additional move to a temporary together with clearing xor is needed.

2022-04-29  Uroš Bizjak  <ubizjak@gmail.com>

gcc/ChangeLog:

	PR target/51954
	* config/i386/i386.md (adcl/neg -> sbb peephole): New peephole2.
gcc/testsuite/ChangeLog:

	PR target/51954
	* gcc.target/i386/pr51954.c: New test.

diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index c74edd1aaef38672b7e207f7b273e61db9c166c3..b321cda1f22f75af03813dd26cce3a738dd5e8b4 100644 (file)
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -10929,6 +10929,50 @@
      (clobber (reg:CC FLAGS_REG))])]
   "split_double_mode (<DWI>mode, &operands[0], 2, &operands[0], &operands[2]);")
 
+;; Convert:
+;;   mov %esi, %edx
+;;   negl %eax
+;;   adcl $0, %edx
+;;   negl %edx
+;; to:
+;;   xorl %edx, %edx
+;;   negl %eax
+;;   sbbl %esi, %edx
+
+(define_peephole2
+  [(set (match_operand:SWI48 0 "general_reg_operand")
+       (match_operand:SWI48 1 "nonimmediate_gr_operand"))
+   (parallel
+    [(set (reg:CCC FLAGS_REG)
+         (ne:CCC (match_operand:SWI48 2 "general_reg_operand") (const_int 0)))
+     (set (match_dup 2) (neg:SWI48 (match_dup 2)))])
+   (parallel
+    [(set (match_dup 0)
+         (plus:SWI48 (plus:SWI48
+                       (ltu:SWI48 (reg:CC FLAGS_REG) (const_int 0))
+                       (match_dup 0))
+                     (const_int 0)))
+     (clobber (reg:CC FLAGS_REG))])
+   (parallel
+    [(set (match_dup 0)
+         (neg:SWI48 (match_dup 0)))
+     (clobber (reg:CC FLAGS_REG))])]
+  "REGNO (operands[0]) != REGNO (operands[2])
+   && !reg_mentioned_p (operands[0], operands[1])
+   && !reg_mentioned_p (operands[2], operands[1])"
+  [(parallel
+    [(set (reg:CCC FLAGS_REG)
+         (ne:CCC (match_dup 2) (const_int 0)))
+     (set (match_dup 2) (neg:SWI48 (match_dup 2)))])
+   (parallel
+    [(set (match_dup 0)
+         (minus:SWI48 (minus:SWI48
+                        (match_dup 0)
+                        (ltu:SWI48 (reg:CC FLAGS_REG) (const_int 0)))
+                      (match_dup 1)))
+     (clobber (reg:CC FLAGS_REG))])]
+  "ix86_expand_clear (operands[0]);")
+
 (define_insn "*neg<mode>_1"
   [(set (match_operand:SWI 0 "nonimmediate_operand" "=<r>m")
        (neg:SWI (match_operand:SWI 1 "nonimmediate_operand" "0")))

diff --git a/gcc/testsuite/gcc.target/i386/pr51954.c b/gcc/testsuite/gcc.target/i386/pr51954.c
new file mode 100644 (file)
index 0000000..5e757de
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr51954.c
@@ -0,0 +1,15 @@
+/* PR target/51954 */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+/* { dg-final { scan-assembler-not "adc" } } */
+
+#ifdef __x86_64__
+#define TYPE __int128
+#else
+#define TYPE long long
+#endif
+
+TYPE bar (TYPE x)
+{
+  return -x;
+}