[PATCH] D78547: [TTI] getUserCost to return getCastInstrCost

[Sanjay Patel via Phabricator via llvm-commits]

spatel added inline comments.


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Comment at: llvm/test/Analysis/CostModel/X86/size-cost.ll:33
 ; CHECK-LABEL: 'bitcast_f64_i64'
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %r = bitcast double %x to i64
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %r = bitcast double %x to i64
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: ret i64 %r
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lebedev.ri wrote:
> spatel wrote:
> > samparker wrote:
> > > spatel wrote:
> > > > Let me know if I'm missing larger context, but this is not correct. A cast from xmm <-> gpr ("movq %xmm0, %rax") is not free in any sense on any x86 target AFAIK.
> > > > 
> > > > Do we need to fix the x86 override as a preliminary step?
> > > I didn't expect it to be correct.. I'm happy to look into the fix.
> > Sounds good - thanks!
> Is it thought? Note that we test *size* cost here.
> Does `bitcast` instruction itself actually has size cost?
> (does it get lowered to any assembly instructions?)
I was assuming this and the other test requires one of:
  movq %xmm0, %rax
  movq %rax, %xmm0


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  https://reviews.llvm.org/D78547/new/

https://reviews.llvm.org/D78547