From ad803a967a6c18ae3bd6f8381ebc8a78c31a82ae Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Tue, 3 Dec 2019 15:27:51 -0800
Subject: [PATCH] i386: Use add for a = a + b and a = b + a when possible
Since except for Bonnell,
01 fb add %edi,%ebx
is faster and shorter than
8d 1c 1f lea (%rdi,%rbx,1),%ebx
we should use add for a = a + b and a = b + a when possible if not
optimizing for Bonnell.
Tested on x86-64.
gcc/
PR target/92807
* config/i386/i386.c (ix86_lea_outperforms): Check !TARGET_BONNELL.
(ix86_avoid_lea_for_addr): When not optimizing for Bonnell, use add
for a = a + b and a = b + a.
gcc/testsuite/
PR target/92807
* gcc.target/i386/pr92807-1.c: New test.
---
gcc/config/i386/i386.c | 27 +++++++++++++++--------
gcc/testsuite/gcc.target/i386/pr92807-1.c | 11 +++++++++
2 files changed, 29 insertions(+), 9 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/i386/pr92807-1.c
@@ -14393,11 +14393,10 @@ ix86_lea_outperforms (rtx_insn *insn, unsigned int regno0, unsigned int regno1,
{
int dist_define, dist_use;
- /* For Silvermont if using a 2-source or 3-source LEA for
- non-destructive destination purposes, or due to wanting
- ability to use SCALE, the use of LEA is justified. */
- if (TARGET_SILVERMONT || TARGET_GOLDMONT || TARGET_GOLDMONT_PLUS
- || TARGET_TREMONT || TARGET_INTEL)
+ /* For Atom processors newer than Bonnell, if using a 2-source or
+ 3-source LEA for non-destructive destination purposes, or due to
+ wanting ability to use SCALE, the use of LEA is justified. */
+ if (!TARGET_BONNELL)
{
if (has_scale)
return true;
@@ -14532,10 +14531,6 @@ ix86_avoid_lea_for_addr (rtx_insn *insn, rtx operands[])
struct ix86_address parts;
int ok;
- /* Check we need to optimize. */
- if (!TARGET_AVOID_LEA_FOR_ADDR || optimize_function_for_size_p (cfun))
- return false;
-
/* The "at least two components" test below might not catch simple
move or zero extension insns if parts.base is non-NULL and parts.disp
is const0_rtx as the only components in the address, e.g. if the
@@ -14572,6 +14567,20 @@ ix86_avoid_lea_for_addr (rtx_insn *insn, rtx operands[])
if (parts.index)
regno2 = true_regnum (parts.index);
+ /* Use add for a = a + b and a = b + a since it is faster and shorter
+ than lea for most processors. For the processors like BONNELL, if
+ the destination register of LEA holds an actual address which will
+ be used soon, LEA is better and otherwise ADD is better. */
+ if (!TARGET_BONNELL
+ && parts.scale == 1
+ && (!parts.disp || parts.disp == const0_rtx)
+ && (regno0 == regno1 || regno0 == regno2))
+ return true;
+
+ /* Check we need to optimize. */
+ if (!TARGET_AVOID_LEA_FOR_ADDR || optimize_function_for_size_p (cfun))
+ return false;
+
split_cost = 0;
/* Compute how many cycles we will add to execution time
new file mode 100644
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+unsigned int
+abs2 (unsigned int a)
+{
+ unsigned int s = ((a>>15)&0x10001)*0xffff;
+ return (a+s)^s;
+}
+
+/* { dg-final { scan-assembler-not "leal" } } */
--
2.21.0