[llvm-commits] [llvm] r141353 - in /llvm/trunk: lib/Target/X86/X86InstrInfo.td lib/Target/X86/X86RegisterInfo.td test/MC/X86/x86-32.s test/MC/X86/x86-64.s utils/TableGen/X86DisassemblerTables.cpp

Eli Friedman eli.friedman at gmail.com
Thu Oct 6 23:41:19 PDT 2011 

On Thu, Oct 6, 2011 at 11:33 PM, Craig Topper <craig.topper at gmail.com> wrote:
> On Thu, Oct 6, 2011 at 11:26 PM, Eli Friedman <eli.friedman at gmail.com>
> wrote:
>>
>> On Thu, Oct 6, 2011 at 10:35 PM, Craig Topper <craig.topper at gmail.com>
>> wrote:
>> > Author: ctopper
>> > Date: Fri Oct  7 00:35:38 2011
>> > New Revision: 141353
>> >
>> > URL: http://llvm.org/viewvc/llvm-project?rev=141353&view=rev
>> > Log:
>> > Revert part of r141274. Only need to change encoding for xchg %eax, %eax
>> > in 64-bit mode. This is because in 64-bit mode xchg %eax, %eax implies
>> > zeroing the upper 32-bits of RAX which makes it not a NOP. In 32-bit mode
>> > using NOP encoding is fine.
>> >
>> > Modified:
>> >    llvm/trunk/lib/Target/X86/X86InstrInfo.td
>> >    llvm/trunk/lib/Target/X86/X86RegisterInfo.td
>> >    llvm/trunk/test/MC/X86/x86-32.s
>> >    llvm/trunk/test/MC/X86/x86-64.s
>> >    llvm/trunk/utils/TableGen/X86DisassemblerTables.cpp
>> >
>> > Modified: llvm/trunk/lib/Target/X86/X86InstrInfo.td
>> > URL:
>> > http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86InstrInfo.td?rev=141353&r1=141352&r2=141353&view=diff
>> >
>> > ==============================================================================
>> > --- llvm/trunk/lib/Target/X86/X86InstrInfo.td (original)
>> > +++ llvm/trunk/lib/Target/X86/X86InstrInfo.td Fri Oct  7 00:35:38 2011
>> > @@ -1154,11 +1154,15 @@
>> >                   "xchg{q}\t{$val, $src|$src, $val}", []>;
>> >  }
>> >
>> > -def XCHG16ar : I<0x90, AddRegFrm, (outs), (ins GR16_NOAX:$src),
>> > +def XCHG16ar : I<0x90, AddRegFrm, (outs), (ins GR16:$src),
>> >                   "xchg{w}\t{$src, %ax|AX, $src}", []>, OpSize;
>> > -def XCHG32ar : I<0x90, AddRegFrm, (outs), (ins GR32_NOAX:$src),
>> > -                  "xchg{l}\t{$src, %eax|EAX, $src}", []>;
>> > -def XCHG64ar : RI<0x90, AddRegFrm, (outs), (ins GR64_NOAX:$src),
>> > +def XCHG32ar : I<0x90, AddRegFrm, (outs), (ins GR32:$src),
>> > +                  "xchg{l}\t{$src, %eax|EAX, $src}", []>,
>> > Requires<[In32BitMode]>;
>> > +// Uses GR32_NOAX in 64-bit mode to prevent encoding using the 0x90 NOP
>> > encoding.
>> > +// xchg %eax, %eax needs to clear upper 32-bits of RAX so is not a NOP.
>> > +def XCHG32ar64 : I<0x90, AddRegFrm, (outs), (ins GR32_NOAX:$src),
>> > +                   "xchg{l}\t{$src, %eax|EAX, $src}", []>,
>> > Requires<[In64BitMode]>;
>> > +def XCHG64ar : RI<0x90, AddRegFrm, (outs), (ins GR64:$src),
>> >                   "xchg{q}\t{$src, %rax|RAX, $src}", []>;
>> >
>> >
>> > @@ -1716,6 +1720,7 @@
>> >  def : InstAlias<"xchgq $mem, $val", (XCHG64rm GR64:$val, i64mem:$mem)>;
>> >
>> >  // xchg: We accept "xchgX <reg>, %eax" and "xchgX %eax, <reg>" as
>> > synonyms.
>> > -def : InstAlias<"xchgw %ax, $src", (XCHG16ar GR16_NOAX:$src)>;
>> > -def : InstAlias<"xchgl %eax, $src", (XCHG32ar GR32_NOAX:$src)>;
>> > -def : InstAlias<"xchgq %rax, $src", (XCHG64ar GR64_NOAX:$src)>;
>> > +def : InstAlias<"xchgw %ax, $src", (XCHG16ar GR16:$src)>;
>> > +def : InstAlias<"xchgl %eax, $src", (XCHG32ar GR32:$src)>,
>> > Requires<[In32BitMode]>;
>> > +def : InstAlias<"xchgl %eax, $src", (XCHG32ar64 GR32_NOAX:$src)>,
>> > Requires<[In64BitMode]>;
>> > +def : InstAlias<"xchgq %rax, $src", (XCHG64ar GR64:$src)>;
>> >
>> > Modified: llvm/trunk/lib/Target/X86/X86RegisterInfo.td
>> > URL:
>> > http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86RegisterInfo.td?rev=141353&r1=141352&r2=141353&view=diff
>> >
>> > ==============================================================================
>> > --- llvm/trunk/lib/Target/X86/X86RegisterInfo.td (original)
>> > +++ llvm/trunk/lib/Target/X86/X86RegisterInfo.td Fri Oct  7 00:35:38
>> > 2011
>> > @@ -390,21 +390,11 @@
>> >                        (GR32_NOREX sub_32bit)];
>> >  }
>> >
>> > -// GR16_NOAX - GR16 registers except AX.
>> > -def GR16_NOAX : RegisterClass<"X86", [i16], 16, (sub GR16, AX)> {
>> > -  let SubRegClasses = [(GR8 sub_8bit, sub_8bit_hi)];
>> > -}
>> > -
>> > -// GR32_NOAX - GR32 registers except EAX.
>> > +// GR32_NOAX - GR32 registers except EAX. Used by AddRegFrm of XCHG32
>> > in 64-bit
>> > +// mode to prevent encoding using the 0x90 NOP encoding. xchg %eax,
>> > %eax needs
>> > +// to clear upper 32-bits of RAX so is not a NOP.
>> >  def GR32_NOAX : RegisterClass<"X86", [i32], 32, (sub GR32, EAX)> {
>> > -  let SubRegClasses = [(GR8 sub_8bit, sub_8bit_hi), (GR16_NOAX
>> > sub_16bit)];
>> > -}
>> > -
>> > -// GR64_NOAX - GR64 registers except RAX.
>> > -def GR64_NOAX : RegisterClass<"X86", [i64], 64, (sub GR64, RAX)> {
>> > -  let SubRegClasses = [(GR8 sub_8bit, sub_8bit_hi),
>> > -                       (GR16_NOAX sub_16bit),
>> > -                       (GR32_NOAX sub_32bit)];
>> > +  let SubRegClasses = [(GR8 sub_8bit, sub_8bit_hi), (GR16 sub_16bit)];
>> >  }
>> >
>> >  // GR32_NOSP - GR32 registers except ESP.
>> >
>> > Modified: llvm/trunk/test/MC/X86/x86-32.s
>> > URL:
>> > http://llvm.org/viewvc/llvm-project/llvm/trunk/test/MC/X86/x86-32.s?rev=141353&r1=141352&r2=141353&view=diff
>> >
>> > ==============================================================================
>> > --- llvm/trunk/test/MC/X86/x86-32.s (original)
>> > +++ llvm/trunk/test/MC/X86/x86-32.s Fri Oct  7 00:35:38 2011
>> > @@ -948,11 +948,11 @@
>> >
>> >  // PR10345
>> >  // CHECK: xchgl %eax, %eax
>> > -// CHECK: encoding: [0x87,0xc0]
>> > +// CHECK: encoding: [0x90]
>> >  xchgl %eax, %eax
>> >
>> >  // CHECK: xchgw %ax, %ax
>> > -// CHECK: encoding: [0x66,0x87,0xc0]
>> > +// CHECK: encoding: [0x66,0x90]
>> >  xchgw %ax, %ax
>> >
>> >  // CHECK: xchgl %ecx, %eax
>> >
>> > Modified: llvm/trunk/test/MC/X86/x86-64.s
>> > URL:
>> > http://llvm.org/viewvc/llvm-project/llvm/trunk/test/MC/X86/x86-64.s?rev=141353&r1=141352&r2=141353&view=diff
>> >
>> > ==============================================================================
>> > --- llvm/trunk/test/MC/X86/x86-64.s (original)
>> > +++ llvm/trunk/test/MC/X86/x86-64.s Fri Oct  7 00:35:38 2011
>> > @@ -1173,7 +1173,7 @@
>> >
>> >  // PR10345
>> >  // CHECK: xchgq %rax, %rax
>> > -// CHECK: encoding: [0x48,0x87,0xc0]
>> > +// CHECK: encoding: [0x48,0x90]
>> >  xchgq %rax, %rax
>> >
>> >  // CHECK: xchgl %eax, %eax
>> > @@ -1181,7 +1181,7 @@
>> >  xchgl %eax, %eax
>> >
>> >  // CHECK: xchgw %ax, %ax
>> > -// CHECK: encoding: [0x66,0x87,0xc0]
>> > +// CHECK: encoding: [0x66,0x90]
>> >  xchgw %ax, %ax
>>
>> Close, but not quite: 0x66 0x90 is a NOP, not xchgw on x86-64.
>>
>> -Eli
>
>  I'm not sure I'm following. Are you saying it should be 0x66 0x87 0xc0 or
> just that the string for the CHECK is wrong?

It should be 0x66 0x87 0xc0; you can double-check with binutils as...

-Eli

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