[PATCH] D118183: Fix UB in DwarfExpression::emitLegacyZExt()

Wed Jan 26 12:47:15 PST 2022

xbolva00 added inline comments.

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Comment at: llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp:686
+  // A ULEB can encode 7 1-bits per byte.
+  if (FromBits / 7 < 1+1+1+1+1) {
+    // (X & (1 << FromBits - 1))
----------------
JDevlieghere wrote:
> I had some trouble figuring out what the `1+1+1+1+1` was supposed to represent. In case anyone is wondering it's 1 byte per DWARF opcode and 1 byte for the small ULEB128 in the alternative encoding below. Maybe we should make that more clear in the comment or used a named temporary/
> 
> Also, should we use `(FromBits+6)/7` to ensure we always round up? 
Agree with you. This should be reworked /commented more.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D118183/new/

https://reviews.llvm.org/D118183