[llvm] c35e818 - [GVN][NFC] Remove redundant check

[via llvm-commits]

Author: ksyx
Date: 2021-11-13T15:59:43-05:00
New Revision: c35e8185d8c170c20e28956e0c9f3c1be895fefb

URL: https://github.com/llvm/llvm-project/commit/c35e8185d8c170c20e28956e0c9f3c1be895fefb
DIFF: https://github.com/llvm/llvm-project/commit/c35e8185d8c170c20e28956e0c9f3c1be895fefb.diff

LOG: [GVN][NFC] Remove redundant check

The if-check above deleted part guarantees that StoreOffset <= LoadOffset
and that StoreOffset + StoreSize >= LoadOffset + LoadSize, and given that
LoadOffset + LoadSize > LoadOffset when LoadSize > 0. Thus, this shows
StoreOffset + StoreSize > LoadOffset is guaranteed given LoadSize > 0,
while it could be meaningless to have a type with nonpositive size, so that
the check could be removed.

Part of revision D100179
Reviewed By: nikic

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/lib/Transforms/Utils/VNCoercion.cpp b/llvm/lib/Transforms/Utils/VNCoercion.cpp
index dbe3cc93e72b4..9984b83c3ff0c 100644
--- a/llvm/lib/Transforms/Utils/VNCoercion.cpp
+++ b/llvm/lib/Transforms/Utils/VNCoercion.cpp
@@ -204,18 +204,6 @@ static int analyzeLoadFromClobberingWrite(Type *LoadTy, Value *LoadPtr,
       StoreOffset + StoreSize < LoadOffset + LoadSize)
     return -1;
 
-  // If the load and store are to the exact same address, they should have been
-  // a must alias.  AA must have gotten confused.
-  // FIXME: Study to see if/when this happens.  One case is forwarding a memset
-  // to a load from the base of the memset.
-
-  // If the load and store don't overlap at all, the store doesn't provide
-  // anything to the load.  In this case, they really don't alias at all, AA
-  // must have gotten confused.  The if statement above ensure the condition
-  // that StoreOffset <= LoadOffset.
-  if (StoreOffset + int64_t(StoreSize) <= LoadOffset)
-    return -1;
-
   // Okay, we can do this transformation.  Return the number of bytes into the
   // store that the load is.
   return LoadOffset - StoreOffset;