From: H.J. Lu Date: Thu, 18 Dec 2014 17:35:45 +0000 (+0000) Subject: X86-64: Add -mskip-rax-setup X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=fbe575b652f5bdcc459f447a0e6f0e059996d4ef;p=gcc.git 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. From-SVN: r218870 --- diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 1fd5b4f6f1a..6e7cfebb7d9 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,11 @@ +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. + 2014-12-18 Alan Lawrence * config/aarch64/aarch64-simd.md (aarch64_lshr_simddi): Handle shift diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c index 17ef75117ff..122a350d99d 100644 --- a/gcc/config/i386/i386.c +++ b/gcc/config/i386/i386.c @@ -25461,7 +25461,12 @@ ix86_expand_call (rtx retval, rtx fnaddr, rtx callarg1, } } - 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 3d54bfa1945..6dc4da280bb 100644 --- a/gcc/config/i386/i386.opt +++ b/gcc/config/i386/i386.opt @@ -831,6 +831,10 @@ Target Report Var(flag_nop_mcount) Init(0) Generate mcount/__fentry__ calls as nops. To activate they need to be patched in. +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 15068da33e4..33a7ed2cfa8 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -16256,6 +16256,19 @@ the profiling functions as nops. This is useful when they should be patched in later dynamically. This is likely only useful together with @option{-mrecord-mcount}. +@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/ChangeLog b/gcc/testsuite/ChangeLog index f7e72ed7a84..4d75d0e04b2 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,9 @@ +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. + 2014-12-18 Alan Lawrence * gcc.target/aarch64/ushr64_1.c: Remove scan-assembler "ushr...64". 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; +}