On Fri, Apr 22, 2016 at 6:03 AM, Uros Bizjak <ubiz...@gmail.com> wrote:
> On Fri, Apr 22, 2016 at 2:54 PM, H.J. Lu <hjl.to...@gmail.com> wrote:
>> For -fno-plt, we load the external function address via the GOT slot
>> so that linker won't create an PLT entry for extern function address.
>>
>> Tested on x86-64. I also built GCC with -fno-plt. It removes 99% PLT
>> entries. OK for trunk?
>>
>> H.J.
>> --
>> gcc/
>>
>> PR target/pr67400
>> * config/i386/i386-protos.h (ix86_force_load_from_GOT_p): New.
>> * config/i386/i386.c (ix86_force_load_from_GOT_p): New function.
>> (ix86_legitimate_address_p): Allow UNSPEC_GOTPCREL for
>> ix86_force_load_from_GOT_p returns true.
>> (ix86_print_operand_address): Support UNSPEC_GOTPCREL if
>> ix86_force_load_from_GOT_p returns true.
>> (ix86_expand_move): Load the external function address via the
>> GOT slot if ix86_force_load_from_GOT_p returns true.
>> * config/i386/predicates.md (x86_64_immediate_operand): Return
>> false if ix86_force_load_from_GOT_p returns true.
>>
>> gcc/testsuite/
>>
>> PR target/pr67400
>> * gcc.target/i386/pr67400-1.c: New test.
>> * gcc.target/i386/pr67400-2.c: Likewise.
>> * gcc.target/i386/pr67400-3.c: Likewise.
>> * gcc.target/i386/pr67400-4.c: Likewise.
>
> Please get someone that knows this linker magic to review the
> functionality first. Maybe Jakub can help?
>
Hi Jakub,
Can you review this patch?
Thanks.
--
H.J.
From 3c81d37bb422f9856b373c63dfc6e19e035a7714 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.to...@gmail.com>
Date: Fri, 28 Aug 2015 19:14:49 -0700
Subject: [PATCH] Load external function address via GOT slot
For -fno-plt, we load the external function address via the GOT slot
so that linker won't create an PLT entry for extern function address.
gcc/
PR target/67400
* config/i386/i386-protos.h (ix86_force_load_from_GOT_p): New.
* config/i386/i386.c (ix86_force_load_from_GOT_p): New function.
(ix86_legitimate_address_p): Allow UNSPEC_GOTPCREL if
ix86_force_load_from_GOT_p returns true.
(ix86_print_operand_address): Support UNSPEC_GOTPCREL if
ix86_force_load_from_GOT_p returns true.
(ix86_expand_move): Load the external function address via the
GOT slot if ix86_force_load_from_GOT_p returns true.
* config/i386/predicates.md (x86_64_immediate_operand): Return
false if ix86_force_load_from_GOT_p returns true.
gcc/testsuite/
PR target/67400
* gcc.target/i386/pr67400-1.c: New test.
* gcc.target/i386/pr67400-2.c: Likewise.
* gcc.target/i386/pr67400-3.c: Likewise.
* gcc.target/i386/pr67400-4.c: Likewise.
---
gcc/config/i386/i386-protos.h | 1 +
gcc/config/i386/i386.c | 42 +++++++++++++++++++++++++++++++
gcc/config/i386/predicates.md | 4 +++
gcc/testsuite/gcc.target/i386/pr67400-1.c | 13 ++++++++++
gcc/testsuite/gcc.target/i386/pr67400-2.c | 14 +++++++++++
gcc/testsuite/gcc.target/i386/pr67400-3.c | 16 ++++++++++++
gcc/testsuite/gcc.target/i386/pr67400-4.c | 13 ++++++++++
7 files changed, 103 insertions(+)
create mode 100644 gcc/testsuite/gcc.target/i386/pr67400-1.c
create mode 100644 gcc/testsuite/gcc.target/i386/pr67400-2.c
create mode 100644 gcc/testsuite/gcc.target/i386/pr67400-3.c
create mode 100644 gcc/testsuite/gcc.target/i386/pr67400-4.c
diff --git a/gcc/config/i386/i386-protos.h b/gcc/config/i386/i386-protos.h
index 447f67e..99775cb 100644
--- a/gcc/config/i386/i386-protos.h
+++ b/gcc/config/i386/i386-protos.h
@@ -70,6 +70,7 @@ extern bool ix86_expand_set_or_movmem (rtx, rtx, rtx, rtx, rtx, rtx,
extern bool constant_address_p (rtx);
extern bool legitimate_pic_operand_p (rtx);
extern bool legitimate_pic_address_disp_p (rtx);
+extern bool ix86_force_load_from_GOT_p (rtx);
extern void print_reg (rtx, int, FILE*);
extern void ix86_print_operand (FILE *, rtx, int);
diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 05476f3..6d73651 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -14833,6 +14833,24 @@ ix86_legitimate_constant_p (machine_mode mode, rtx x)
return true;
}
+/* True if operand X should be loaded from GOT. */
+
+bool
+ix86_force_load_from_GOT_p (rtx x)
+{
+ /* External function symbol should be loaded via the GOT slot for
+ -fno-plt. */
+ return (!flag_plt
+ && !flag_pic
+ && ix86_cmodel != CM_LARGE
+ && TARGET_64BIT
+ && !TARGET_PECOFF
+ && !TARGET_MACHO
+ && GET_CODE (x) == SYMBOL_REF
+ && SYMBOL_REF_FUNCTION_P (x)
+ && !SYMBOL_REF_LOCAL_P (x));
+}
+
/* Determine if it's legal to put X into the constant pool. This
is not possible for the address of thread-local symbols, which
is checked above. */
@@ -15213,6 +15231,10 @@ ix86_legitimate_address_p (machine_mode, rtx addr, bool strict)
return false;
case UNSPEC_GOTPCREL:
+ gcc_assert (flag_pic
+ || ix86_force_load_from_GOT_p (XVECEXP (XEXP (disp, 0), 0, 0)));
+ goto is_legitimate_pic;
+
case UNSPEC_PCREL:
gcc_assert (flag_pic);
goto is_legitimate_pic;
@@ -17817,6 +17839,11 @@ ix86_print_operand_address_as (FILE *file, rtx addr,
}
else if (flag_pic)
output_pic_addr_const (file, disp, 0);
+ else if (GET_CODE (disp) == CONST
+ && GET_CODE (XEXP (disp, 0)) == UNSPEC
+ && XINT (XEXP (disp, 0), 1) == UNSPEC_GOTPCREL
+ && ix86_force_load_from_GOT_p (XVECEXP (XEXP (disp, 0), 0, 0)))
+ output_pic_addr_const (file, XEXP (disp, 0), code);
else
output_addr_const (file, disp);
}
@@ -19082,6 +19109,21 @@ ix86_expand_move (machine_mode mode, rtx operands[])
op1 = convert_to_mode (mode, op1, 1);
}
}
+ }
+ else if (ix86_force_load_from_GOT_p (op1))
+ {
+ /* Load the external function address via the GOT slot to
+ avoid PLT. */
+ op1 = gen_rtx_UNSPEC (Pmode, gen_rtvec (1, op1),
+ (TARGET_64BIT
+ ? UNSPEC_GOTPCREL
+ : UNSPEC_GOT));
+ op1 = gen_rtx_CONST (Pmode, op1);
+ op1 = gen_const_mem (Pmode, op1);
+ op1 = convert_to_mode (mode, op1, 1);
+ /* Force OP1 into register to prevent cse and fwprop from
+ replacing a GOT load with a constant. */
+ op1 = force_reg (mode, op1);
}
else
{
diff --git a/gcc/config/i386/predicates.md b/gcc/config/i386/predicates.md
index b3cf2a3..cd7e20c 100644
--- a/gcc/config/i386/predicates.md
+++ b/gcc/config/i386/predicates.md
@@ -167,6 +167,10 @@
/* TLS symbols are not constant. */
if (SYMBOL_REF_TLS_MODEL (op))
return false;
+ /* Load the external function address via the GOT slot to avoid
+ PLT. */
+ if (ix86_force_load_from_GOT_p (op))
+ return false;
return (ix86_cmodel == CM_SMALL || ix86_cmodel == CM_KERNEL
|| (ix86_cmodel == CM_MEDIUM && !SYMBOL_REF_FAR_ADDR_P (op)));
diff --git a/gcc/testsuite/gcc.target/i386/pr67400-1.c b/gcc/testsuite/gcc.target/i386/pr67400-1.c
new file mode 100644
index 0000000..a875b76
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr67400-1.c
@@ -0,0 +1,13 @@
+/* { dg-do compile { target *-*-linux* } } */
+/* { dg-options "-O2 -fno-pic -fno-plt" } */
+
+extern void bar (void);
+
+void *
+foo (void)
+{
+ return &bar;
+}
+
+/* { dg-final { scan-assembler "mov\(l|q\)\[ \t\]*bar@GOTPCREL" { target { ! ia32 } } } } */
+/* { dg-final { scan-assembler-not "mov\(l|q\)\[ \t\]*\\\$bar," { target { ! ia32 } } } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr67400-2.c b/gcc/testsuite/gcc.target/i386/pr67400-2.c
new file mode 100644
index 0000000..9f3f4bc
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr67400-2.c
@@ -0,0 +1,14 @@
+/* { dg-do compile { target *-*-linux* } } */
+/* { dg-options "-O2 -fno-pic -fno-plt" } */
+
+extern void bar (void);
+extern void *p;
+
+void
+foo (void)
+{
+ p = &bar;
+}
+
+/* { dg-final { scan-assembler "mov\(l|q\)\[ \t\]*bar@GOTPCREL" { target { ! ia32 } } } } */
+/* { dg-final { scan-assembler-not "mov\(l|q\)\[ \t\]*\\\$bar," { target { ! ia32 } } } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr67400-3.c b/gcc/testsuite/gcc.target/i386/pr67400-3.c
new file mode 100644
index 0000000..045974e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr67400-3.c
@@ -0,0 +1,16 @@
+/* { dg-do compile { target *-*-linux* } } */
+/* { dg-options "-O2 -fno-pic -fno-plt" } */
+
+static void
+bar (void)
+{
+}
+
+void *
+foo (void)
+{
+ return &bar;
+}
+
+/* { dg-final { scan-assembler "mov\(l|q\)\[ \t\]*\\\$bar," } } */
+/* { dg-final { scan-assembler-not "mov\(l|q\)\[ \t\]*bar@GOTPCREL" { target { ! ia32 } } } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr67400-4.c b/gcc/testsuite/gcc.target/i386/pr67400-4.c
new file mode 100644
index 0000000..fd373db
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr67400-4.c
@@ -0,0 +1,13 @@
+/* { dg-do compile { target *-*-linux* } } */
+/* { dg-options "-O2 -fno-pic -fno-plt" } */
+
+extern void bar (void) __attribute__ ((visibility ("hidden")));
+
+void *
+foo (void)
+{
+ return &bar;
+}
+
+/* { dg-final { scan-assembler "mov\(l|q\)\[ \t\]*\\\$bar," } } */
+/* { dg-final { scan-assembler-not "mov\(l|q\)\[ \t\]*bar@GOTPCREL" { target { ! ia32 } } } } */
--
2.5.5
