[PATCH] D30919: Salvage debug info from instructions about to be deleted

[Adrian Prantl via Phabricator via llvm-commits]

aprantl added a comment.

Working on an updated version now...



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Comment at: lib/Transforms/Utils/Local.cpp:1366-1375
+  if (auto *BitCast = dyn_cast<BitCastInst>(&I)) {
+    // Bitcasts are entirely irrelevant for debug info. Rewrite the dbg.value to
+    // use the cast's source.
+    findDbgValues(DbgValues, &I);
+    for (auto *DVI : DbgValues) {
+      DVI->setOperand(0, MDWrap(I.getOperand(0)));
+      DEBUG(dbgs() << "SALVAGE: " << *DVI << '\n');
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majnemer wrote:
> Any idea on the perf impact of this change?
I made a fairly unscientific test by compiling running time ninja llc (building a stage2 llc Release+Assert using a Release+Assert compiler) on my iMac and the time difference between with and without this patch is well within the noise.

I also captured the resulting .dSYM bundles and ran dwarfdump | grep -c AT_location on it and it showed a 20% increase of variables with a location (993456/827467).


https://reviews.llvm.org/D30919