[PATCH] D28251: [AArch64] Fix over-eager early-exit in load-store combiner

[Jun Bum Lim via Phabricator via llvm-commits]

junbuml added inline comments.


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Comment at: lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp:1473-1474
   int OffsetStride = IsUnscaled ? getMemScale(MI) : 1;
+  if (Offset > 0)
+    Offset -= OffsetStride;
   if (!inBoundsForPair(IsUnscaled, Offset, OffsetStride))
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In which case, can you see better st/ld pairs with this change ?   Can you add a case if you have? Also, is there a case on which this change cause worse combinations of st/ld pairs? 

In some case, this change may unnecessarily call findMatchingInsn() : 
 e.g., 
  STR %XZR, %X0, 64  <--- we don't even need to try to look up pair for this
  STR %XZR, %X0, 65



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Comment at: test/CodeGen/AArch64/ldst-opt.ll:1418-1421
+; CHECKCOMBINE: // %entry
+; CHECKCOMBINE-NEXT: stp xzr, xzr, [x0]
+; CHECKCOMBINE-NEXT: stp xzr, xzr, [x0, #16]
+; CHECKCOMBINE-NEXT: ret
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For me, this doesn't seem to be related with your change in AArch64LoadStoreOptimizer.cpp
 


https://reviews.llvm.org/D28251