[PATCH] D61671: X86WinAllocaExpander: Drop code looking through register copies (PR41786)

[Reid Kleckner via Phabricator via llvm-commits]

rnk accepted this revision.
rnk added a comment.
This revision is now accepted and ready to land.

lgtm, too



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Comment at: llvm/lib/Target/X86/X86WinAllocaExpander.cpp:91-94
   if (!Def ||
       (Def->getOpcode() != X86::MOV32ri && Def->getOpcode() != X86::MOV64ri) ||
       !Def->getOperand(1).isImm())
     return -1;
----------------
As a follow-up, I think it would be reasonable for WIN_ALLOCA_* to accept either reg or imm operands so we won't need this code at all. Right now we emit this MI:
  %12:gr32 = MOV32ri 12
  WIN_ALLOCA_32 %12:gr32, implicit-def dead $eax, implicit-def dead $esp, implicit-def dead $eflags, implicit $esp

But it's not really necessary, since in the end we're going to make SUB64ri instructions with the immediate.

I think the instruction wasn't designed this way because most truly dynamic allocas do not use a fixed size. It's only inalloca that introduces them.


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  https://reviews.llvm.org/D61671/new/

https://reviews.llvm.org/D61671