From 72345ebb4922b2bf38326dd64692e82dc1d58dd4 Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Wed, 17 Dec 2014 15:16:17 -0800 Subject: [PATCH] X86-64: Add -mskip-rax-setup The Linux kernel never passes floating point arguments around, vararg functions or not. Hence no vector registers are ever used when calling a vararg function. But gcc still dutifully emits an "xor %eax,%eax" before each and every call of a vararg function. Since no callee use that for anything, these instructions are redundant. This patch adds the -mskip-rax-setup option to skip setting up RAX register when SSE is disabled and there are no variable arguments passed in vector registers. Since RAX register is used to avoid unnecessarily saving vector registers on stack when passing variable arguments, the impacts of this option are callees may waste some stack space, misbehave or jump to a random location. GCC 4.4 or newer don't those issues, regardless the RAX register value since they don't check the RAX register value when SSE is disabled. gcc/ * config/i386/i386.c (ix86_expand_call): Skip setting up RAX register for -mskip-rax-setup when there are no parameters passed in vector registers. * config/i386/i386.opt (mskip-rax-setup): New option. * doc/invoke.texi: Document -mskip-rax-setup. gcc/testsuite/ * gcc.target/i386/amd64-abi-7.c: New tests. * gcc.target/i386/amd64-abi-8.c: Likwise. * gcc.target/i386/amd64-abi-9.c: Likwise. --- ChangeLog.skip-rax | 17 +++++++++++ gcc/config/i386/i386.c | 7 ++++- gcc/config/i386/i386.opt | 4 +++ gcc/doc/invoke.texi | 13 ++++++++ gcc/testsuite/gcc.target/i386/amd64-abi-7.c | 46 +++++++++++++++++++++++++++++ gcc/testsuite/gcc.target/i386/amd64-abi-8.c | 18 +++++++++++ gcc/testsuite/gcc.target/i386/amd64-abi-9.c | 18 +++++++++++ 7 files changed, 122 insertions(+), 1 deletion(-) create mode 100644 ChangeLog.skip-rax create mode 100644 gcc/testsuite/gcc.target/i386/amd64-abi-7.c create mode 100644 gcc/testsuite/gcc.target/i386/amd64-abi-8.c create mode 100644 gcc/testsuite/gcc.target/i386/amd64-abi-9.c diff --git a/ChangeLog.skip-rax b/ChangeLog.skip-rax new file mode 100644 index 00000000000..d6ecdf0b8eb --- /dev/null +++ b/ChangeLog.skip-rax @@ -0,0 +1,17 @@ +gcc/ + +2014-12-18 H.J. Lu + + * config/i386/i386.c (ix86_expand_call): Skip setting up RAX + register for -mskip-rax-setup when there are no parameters + passed in vector registers. + * config/i386/i386.opt (mskip-rax-setup): New option. + * doc/invoke.texi: Document -mskip-rax-setup. + +gcc/testsuite/ + +2014-12-18 H.J. Lu + + * gcc.target/i386/amd64-abi-7.c: New tests. + * gcc.target/i386/amd64-abi-8.c: Likwise. + * gcc.target/i386/amd64-abi-9.c: Likwise. diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c index 9b24efce9c2..4db74171f1a 100644 --- a/gcc/config/i386/i386.c +++ b/gcc/config/i386/i386.c @@ -23641,7 +23641,12 @@ ix86_expand_call (rtx retval, rtx fnaddr, rtx callarg1, use_reg (&use, pic_offset_table_rtx); } - if (TARGET_64BIT && INTVAL (callarg2) >= 0) + /* Skip setting up RAX register for -mskip-rax-setup when there are no + parameters passed in vector registers. */ + if (TARGET_64BIT + && (INTVAL (callarg2) > 0 + || (INTVAL (callarg2) == 0 + && (TARGET_SSE || !flag_skip_rax_setup)))) { rtx al = gen_rtx_REG (QImode, AX_REG); emit_move_insn (al, callarg2); diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt index 084a2486353..59a2695b3cd 100644 --- a/gcc/config/i386/i386.opt +++ b/gcc/config/i386/i386.opt @@ -611,6 +611,10 @@ mfentry Target Report Var(flag_fentry) Init(-1) Emit profiling counter call at function entry before prologue. +mskip-rax-setup +Target Report Var(flag_skip_rax_setup) Init(0) +Skip setting up RAX register when passing variable arguments. + m8bit-idiv Target Report Mask(USE_8BIT_IDIV) Save Expand 32bit/64bit integer divide into 8bit unsigned integer divide with run-time check diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index 0b0f0701c9a..9d30212f1c7 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -14532,6 +14532,19 @@ counter call before the prologue. Note: On x86 architectures the attribute @code{ms_hook_prologue} isn't possible at the moment for @option{-mfentry} and @option{-pg}. +@item -mskip-rax-setup +@itemx -mno-skip-rax-setup +@opindex mskip-rax-setup +When generating code for the x86-64 architecture with SSE extensions +disabled, @option{-skip-rax-setup} can be used to skip setting up RAX +register when there are no variable arguments passed in vector registers. + +@strong{Warning:} Since RAX register is used to avoid unnecessarily +saving vector registers on stack when passing variable arguments, the +impacts of this option are callees may waste some stack space, +misbehave or jump to a random location. GCC 4.4 or newer don't have +those issues, regardless the RAX register value. + @item -m8bit-idiv @itemx -mno-8bit-idiv @opindex 8bit-idiv diff --git a/gcc/testsuite/gcc.target/i386/amd64-abi-7.c b/gcc/testsuite/gcc.target/i386/amd64-abi-7.c new file mode 100644 index 00000000000..fcca680a09c --- /dev/null +++ b/gcc/testsuite/gcc.target/i386/amd64-abi-7.c @@ -0,0 +1,46 @@ +/* { dg-do run { target { ! { ia32 } } } } */ +/* { dg-options "-O2 -mno-sse" } */ + +#include +#include + +int n1 = 30; +int n2 = 324; +void *n3 = (void *) &n2; +int n4 = 407; + +int e1; +int e2; +void *e3; +int e4; + +static void +__attribute__((noinline)) +foo (va_list va_arglist) +{ + e2 = va_arg (va_arglist, int); + e3 = va_arg (va_arglist, void *); + e4 = va_arg (va_arglist, int); +} + +static void +__attribute__((noinline)) +test (int a1, ...) +{ + va_list va_arglist; + e1 = a1; + va_start (va_arglist, a1); + foo (va_arglist); + va_end (va_arglist); +} + +int +main () +{ + test (n1, n2, n3, n4); + assert (n1 == e1); + assert (n2 == e2); + assert (n3 == e3); + assert (n4 == e4); + return 0; +} diff --git a/gcc/testsuite/gcc.target/i386/amd64-abi-8.c b/gcc/testsuite/gcc.target/i386/amd64-abi-8.c new file mode 100644 index 00000000000..b25ceec1b80 --- /dev/null +++ b/gcc/testsuite/gcc.target/i386/amd64-abi-8.c @@ -0,0 +1,18 @@ +/* { dg-do compile { target { ! { ia32 } } } } */ +/* { dg-options "-O2 -mno-sse -mskip-rax-setup" } */ +/* { dg-final { scan-assembler-not "xorl\[\\t \]*\\\%eax,\[\\t \]*%eax" } } */ + +void foo (const char *, ...); + +void +test1 (void) +{ + foo ("%d", 20); +} + +int +test2 (void) +{ + foo ("%d", 20); + return 3; +} diff --git a/gcc/testsuite/gcc.target/i386/amd64-abi-9.c b/gcc/testsuite/gcc.target/i386/amd64-abi-9.c new file mode 100644 index 00000000000..4707eb7f1c2 --- /dev/null +++ b/gcc/testsuite/gcc.target/i386/amd64-abi-9.c @@ -0,0 +1,18 @@ +/* { dg-do compile { target { ! { ia32 } } } } */ +/* { dg-options "-O2 -mno-sse -mno-skip-rax-setup" } */ +/* { dg-final { scan-assembler-times "xorl\[\\t \]*\\\%eax,\[\\t \]*%eax" 2 } } */ + +void foo (const char *, ...); + +void +test1 (void) +{ + foo ("%d", 20); +} + +int +test2 (void) +{ + foo ("%d", 20); + return 3; +} -- 2.11.4.GIT