[llvm-commits] [llvm] r40736 - in /llvm/trunk: lib/Target/X86/X86InstrMMX.td lib/Target/X86/X86InstrSSE.td test/CodeGen/X86/constant-pool-remat-0.ll

[Chris Lattner]

Woot, nice!  The codegen looks great on x86-32 also.  I noticed that  
we're apparently not remat'ing loads "flds" and friends on the  
fpstack side, but that doesn't seem very critical.

-Chris

On Aug 29, 2007, at 11:00 PM, Evan Cheng wrote:

> This is done. Now we emit this:
>
> _array:
>          subq    $8, %rsp
>          mulss   LCPI1_0(%rip), %xmm0
>          call    _qux
>          mulss   LCPI1_0(%rip), %xmm0
>          addq    $8, %rsp
>          ret
>
> Evan
>
> On Aug 2, 2007, at 8:50 AM, Chris Lattner wrote:
>
>>> Mark the SSE and MMX load instructions that
>>> X86InstrInfo::isReallyTriviallyReMaterializable knows how to handle
>>> with the isReMaterializable flag so that it is given a chance to
>>> handle
>>> them. Without hoisting constant-pool loads from loops this isn't  
>>> very
>>> visible, though it does keep CodeGen/X86/constant-pool-remat-0.ll
>>> from
>>> making a copy of the constant pool on the stack.
>>>
>>> @@ -0,0 +1,10 @@
>>> +; RUN: llvm-as < %s | llc -march=x86-64 | grep LCPI | wc -l |  
>>> grep 3
>>> +
>>> +declare float @qux(float %y)
>>> +
>>> +define float @array(float %a) {
>>> +  %n = mul float %a, 9.0
>>> +  %m = call float @qux(float %n)
>>> +  %o = mul float %m, 9.0
>>> +  ret float %o
>>> +}
>>
>> Interesting testcase.  I'm now getting:
>>
>> _array:
>>          subq    $8, %rsp
>>          movss   LCPI1_0(%rip), %xmm1
>>          mulss   %xmm1, %xmm0
>>          call    _qux
>>          movss   LCPI1_0(%rip), %xmm1
>>          mulss   %xmm1, %xmm0
>>          addq    $8, %rsp
>>          ret
>>
>> for this.  Both loads should be folded into the mulss's.  Because the
>> load is shared at isel time, this can't be done there, but it can be
>> done after the remat.  Maybe the register allocator needs to call
>> MRegisterInfo::foldMemoryOperand if the remat is a load that has a
>> single use?
>>
>> -Chris
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