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

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


================
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
----------------
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?)


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D78547/new/

https://reviews.llvm.org/D78547