[all-commits] [llvm/llvm-project] 245491: [MC] Disable MCAssembler based constant folding fo...

[Fangrui Song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 245491a9f384e4c53421196533c2a2b693efaf8d
      https://github.com/llvm/llvm-project/commit/245491a9f384e4c53421196533c2a2b693efaf8d
  Author: Fangrui Song <i at maskray.me>
  Date:   2024-05-20 (Mon, 20 May 2024)

  Changed paths:
    M llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

  Log Message:
  -----------
  [MC] Disable MCAssembler based constant folding for DwarfDebug

Related to the poor performance of MCAssembler based constant folding
(see `bool MCExpr::evaluateAsAbsolute(int64_t &Res, const MCAssembler *Asm) const` and
`AttemptToFoldSymbolOffsetDifference`),
commit 9500a5d02e23f9b43294e5f662ac099f8989c0e4 (#91082) caused -O0 -g
compile time regression.

9500a5d02e23f9b43294e5f662ac099f8989c0e4 special cased .eh_frame FDE
emitting. This patch adds a special case to .debug_* emitting as well to
mitigate the rest regression.

The MCAssembler based constant folding strategy should be improved to
remove the two special cases.



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