[llvm] 621c6c8 - [InstCombine] recognizeBSwapOrBitReverseIdiom - cleanup bswap/bitreverse detection loop. NFCI.

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2020-09-30T14:19:18+01:00
New Revision: 621c6c89627972d52796e64a9476a7d05f22f2cd

URL: https://github.com/llvm/llvm-project/commit/621c6c89627972d52796e64a9476a7d05f22f2cd
DIFF: https://github.com/llvm/llvm-project/commit/621c6c89627972d52796e64a9476a7d05f22f2cd.diff

LOG: [InstCombine] recognizeBSwapOrBitReverseIdiom - cleanup bswap/bitreverse detection loop. NFCI.

Early out if both pattern matches have failed (or we don't want them). Fix case of bit index iterator (and avoid Wshadow issue).

Added: 
    

Modified: 
    llvm/lib/Transforms/Utils/Local.cpp

Removed: 
    


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diff  --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index a76dc655ddbf..149755bb88b8 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -3038,18 +3038,20 @@ bool llvm::recognizeBSwapOrBitReverseIdiom(
   // Now, is the bit permutation correct for a bswap or a bitreverse? We can
   // only byteswap values with an even number of bytes.
   unsigned DemandedBW = DemandedTy->getBitWidth();
-  bool OKForBSwap = DemandedBW % 16 == 0, OKForBitReverse = true;
-  for (unsigned i = 0; i < DemandedBW; ++i) {
-    OKForBSwap &=
-        bitTransformIsCorrectForBSwap(BitProvenance[i], i, DemandedBW);
-    OKForBitReverse &=
-        bitTransformIsCorrectForBitReverse(BitProvenance[i], i, DemandedBW);
+  bool OKForBSwap = MatchBSwaps && (DemandedBW % 16) == 0;
+  bool OKForBitReverse = MatchBitReversals;
+  for (unsigned BitIdx = 0;
+       (BitIdx < DemandedBW) && (OKForBSwap || OKForBitReverse); ++BitIdx) {
+    OKForBSwap &= bitTransformIsCorrectForBSwap(BitProvenance[BitIdx], BitIdx,
+                                                DemandedBW);
+    OKForBitReverse &= bitTransformIsCorrectForBitReverse(BitProvenance[BitIdx],
+                                                          BitIdx, DemandedBW);
   }
 
   Intrinsic::ID Intrin;
-  if (OKForBSwap && MatchBSwaps)
+  if (OKForBSwap)
     Intrin = Intrinsic::bswap;
-  else if (OKForBitReverse && MatchBitReversals)
+  else if (OKForBitReverse)
     Intrin = Intrinsic::bitreverse;
   else
     return false;