[PATCH] D86883: [X86] Add support for using fast short rep mov for memcpy lowering.

[Craig Topper via Phabricator via llvm-commits]

craig.topper added inline comments.


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Comment at: llvm/lib/Target/X86/X86ISelLowering.cpp:3112
+  assert(Src.getValueType() == Dst.getValueType());
+  SDValue SizeNode = DAG.getConstant(Flags.getByValSize(), dl, Src.getValueType());
 
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Maybe just use getIntPtrConstant instead of getConstant?


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Comment at: llvm/lib/Target/X86/X86SelectionDAGInfo.cpp:198
   SDValue InFlag;
-  Chain = DAG.getCopyToReg(Chain, dl, CX, Size, InFlag);
+  Chain = DAG.getCopyToReg(
+      Chain, dl, CX,
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yamauchi wrote:
> craig.topper wrote:
> > yamauchi wrote:
> > > craig.topper wrote:
> > > > Is this needed because we're no longer calling this with just constants we fixed the size of?
> > > Do you mean, "is the getCopyToReg call needed"? The size needs to be loaded into the RCX/ECX register for the rep movs instruction and the callers aren't doing that. So, it seems yes. Did you mean in a different way?
> > I was asking why the getZExtOrTrunc was added. do we create memcpy's where the size type isn't the same size as the pointer?
> Without the getZExtOrTrunc, I get this fatal error, for example,
> 
> Cannot copy EAX to RCX
> fatal error: error in backend: Cannot emit physreg copy instruction
> 
> which is coming from X86InstrInfo::copyPhysReg.
> 
> Re: "do we create memcpy's where the size type isn't the same size as the pointer?" yes, it seems so. 
Does that occur with the included test case or some other testing?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D86883/new/

https://reviews.llvm.org/D86883