[PATCH] D156767: [AArch64] [BranchRelaxation] Optimize for hot code size in AArch64 branch relaxation

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added a comment.

It seems that this patch should link to D145211 <https://reviews.llvm.org/D145211>. This patch will address this comment https://reviews.llvm.org/D145211#4537173



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Comment at: llvm/lib/Target/AArch64/AArch64InstrInfo.cpp:286
   RS->enterBasicBlockEnd(MBB);
-  Register Reg = RS->FindUnusedReg(&AArch64::GPR64RegClass);
+  // If X16 is unused, then we can rely on the linker to safely insert the
+  // indirect branch.
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This sentence sounds like the linker needs to do work, but in the majority of cases I think the linker won't need to insert a range extension thunk.

Perhaps:

// If X16 is unused, we can rely on linker range extension thunk in case NewDestBB cannot be reached by a single B (e.g. cross-section).


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Comment at: llvm/lib/Target/AArch64/AArch64InstrInfo.cpp:297
+  // manually insert the indirect branch.
+  Reg = RS->FindUnusedReg(&AArch64::GPR64RegClass);
+  if (Reg != AArch64::NoRegister &&
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Can we use another variable so that we can use `const Register Reg = AArch64::X16;` above and remove `Reg = AArch64::X16;` on L312?


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https://reviews.llvm.org/D156767