Add abs pattern to handle {si,di} mode abs to avoid pmax/cmove conversion (PR92651)

From c0bf64efbcaa989349130b676880cc2ed49fca69 Mon Sep 17 00:00:00 2001
From: hongyuw1 <hongyuw1@intel.com>
Date: Thu, 28 Nov 2019 12:49:04 +0000
Subject: [PATCH] Add abs pattern to handle {si,di} mode abs to avoid
 pmax/cmove conversion.

    gcc/
	PR target/92651
	* config/i386/i386.h (TARGET_USE_SIMPLE_ABS_PATTERN): New macro.
	* config/i386/x86-tune.def (X86_TUNE_USE_SIMPLE_ABS_PATTERN): New.
	* config/i386/i386.md (abs<SWI48x>2): New define_expand.

    gcc/testsuite
	* gcc.target/i386/pr92651.c: New testcase.
---
 gcc/config/i386/i386.h                  |  2 ++
 gcc/config/i386/i386.md                 | 39 +++++++++++++++++++++++++
 gcc/config/i386/x86-tune.def            |  7 +++++
 gcc/testsuite/gcc.target/i386/pr92651.c | 16 ++++++++++
 4 files changed, 64 insertions(+)
 create mode 100644 gcc/testsuite/gcc.target/i386/pr92651.c

diff --git a/gcc/config/i386/i386.h b/gcc/config/i386/i386.h
index 108456b14d4..ea27526e42e 100644
--- a/gcc/config/i386/i386.h
+++ b/gcc/config/i386/i386.h
@@ -596,6 +596,8 @@  extern unsigned char ix86_tune_features[X86_TUNE_LAST];
 	ix86_tune_features[X86_TUNE_USE_XCHG_FOR_ATOMIC_STORE]
 #define TARGET_EMIT_VZEROUPPER \
 	ix86_tune_features[X86_TUNE_EMIT_VZEROUPPER]
+#define TARGET_USE_SIMPLE_ABS_PATTERN \
+	ix86_tune_features[X86_TUNE_USE_SIMPLE_ABS_PATTERN]
 
 /* Feature tests against the various architecture variations.  */
 enum ix86_arch_indices {
diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 7ff5872ba43..8e5059aedec 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -9668,6 +9668,45 @@ 
   "#"
   [(set_attr "isa" "noavx,noavx,avx,avx")])
 
+;; Special expand pattern to handle integer mode abs
+
+(define_expand "abs<mode>2"
+  [(set (match_operand:SWI48x 0 "register_operand")
+    (abs:SWI48x
+      (match_operand:SWI48x 1 "register_operand")))]
+  "TARGET_USE_SIMPLE_ABS_PATTERN"
+  {
+    machine_mode mode = <MODE>mode;
+
+    /* Generate rtx abs using abs (x) = (((signed) x >> (W-1)) ^ x) -
+       ((signed) x >> (W-1)) */
+    rtx shift_amount = gen_int_shift_amount (mode,
+				       GET_MODE_PRECISION (mode)
+				       - 1);
+    shift_amount = convert_modes (E_QImode, GET_MODE (shift_amount),
+			    shift_amount, 1);
+    rtx shift_dst = gen_reg_rtx (mode);
+    rtx shift_op = gen_rtx_SET (shift_dst,
+			  gen_rtx_fmt_ee (ASHIFTRT, mode,
+					  operands[1], shift_amount));
+    rtx clobber = gen_rtx_CLOBBER (VOIDmode, gen_rtx_REG (CCmode,
+						    FLAGS_REG));
+    emit_insn (gen_rtx_PARALLEL (VOIDmode, gen_rtvec (2, shift_op,
+						clobber)));
+
+    rtx xor_op = gen_rtx_SET (operands[0],
+			gen_rtx_fmt_ee (XOR, mode, shift_dst,
+					operands[1]));
+    emit_insn (gen_rtx_PARALLEL (VOIDmode, gen_rtvec (2, xor_op, clobber)));
+
+    rtx minus_op = gen_rtx_SET (operands[0],
+			  gen_rtx_fmt_ee (MINUS, mode,
+					  operands[0], shift_dst));
+    emit_insn (gen_rtx_PARALLEL (VOIDmode, gen_rtvec (2, minus_op,
+						clobber)));
+    DONE;
+  })
+
 (define_expand "<code><mode>2"
   [(set (match_operand:X87MODEF 0 "register_operand")
 	(absneg:X87MODEF (match_operand:X87MODEF 1 "register_operand")))]
diff --git a/gcc/config/i386/x86-tune.def b/gcc/config/i386/x86-tune.def
index 328535d38d7..86ff24122e6 100644
--- a/gcc/config/i386/x86-tune.def
+++ b/gcc/config/i386/x86-tune.def
@@ -317,6 +317,13 @@  DEF_TUNE (X86_TUNE_ONE_IF_CONV_INSN, "one_if_conv_insn",
 DEF_TUNE (X86_TUNE_USE_XCHG_FOR_ATOMIC_STORE, "use_xchg_for_atomic_store",
 	 m_CORE_ALL | m_BDVER | m_ZNVER | m_GENERIC)
 
+/* X86_TUNE_USE_SIMPLE_ABS_PATTERN: This enables a new abs pattern by
+   generating instructions for abs (x) = (((signed) x >> (W-1) ^ x) -
+   (signed) x >> (W-1)) instead of cmove or SSE max/abs instructions.  */
+DEF_TUNE (X86_TUNE_USE_SIMPLE_ABS_PATTERN, "use_simple_abs_pattern",
+	  m_CORE_ALL | m_SILVERMONT | m_KNL | m_KNM | m_GOLDMONT
+	  | m_GOLDMONT_PLUS | m_TREMONT )
+
 /*****************************************************************************/
 /* 387 instruction selection tuning                                          */
 /*****************************************************************************/
diff --git a/gcc/testsuite/gcc.target/i386/pr92651.c b/gcc/testsuite/gcc.target/i386/pr92651.c
new file mode 100644
index 00000000000..3d0c3c7bf4e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr92651.c
@@ -0,0 +1,16 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2 -march=corei7" } */
+
+#include <stdlib.h>
+
+int foo(unsigned char a, unsigned char b)
+{
+    int isum=abs(a - b);
+    return isum;
+}
+
+/* { dg-final { scan-assembler-not "cmov*" } } */
+/* { dg-final { scan-assembler "(cltd|cdq|shr)" } } */
+/* { dg-final { scan-assembler-times "xor" 1 } } */
+/* { dg-final { scan-assembler-times "sub" 2 } } */
+
-- 
2.19.1