[llvm] [MCA][X86] Pretend To Have a Stack Engine (PR #153348)

[Andrea Di Biagio via llvm-commits]

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@@ -36,11 +36,31 @@ void X86InstrPostProcess::setMemBarriers(std::unique_ptr<Instruction> &Inst,
   }
 }
 
+void X86InstrPostProcess::useStackEngine(std::unique_ptr<Instruction> &Inst,
+                                         const MCInst &MCI) {
+  if (X86::isPOP(MCI.getOpcode())) {
+    assert(Inst->getUses().size() == 1 &&
+           "Expected pop instruction to only use stack pointer register");
+    Inst->getUses().clear();
+  }
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adibiagio wrote:

I don't remember the custom-behaviour / instr postprocess mechanism.
However, can we add artificial dependencies (similar to chain deps in DAG) for POP instructions, so that they are always guaranteed to executed in-order? Maybe @mshockwave  knows the answer to it.

https://github.com/llvm/llvm-project/pull/153348