[llvm] e244f86 - [VNCoercion] avoid creating bitcast for zero offsets [NFCI]

[Jameson Nash via llvm-commits]

Author: Jameson Nash
Date: 2020-07-13T21:44:17-04:00
New Revision: e244f86f4dfd9e8982940d09294af522d3809d7f

URL: https://github.com/llvm/llvm-project/commit/e244f86f4dfd9e8982940d09294af522d3809d7f
DIFF: https://github.com/llvm/llvm-project/commit/e244f86f4dfd9e8982940d09294af522d3809d7f.diff

LOG: [VNCoercion] avoid creating bitcast for zero offsets [NFCI]

This could previously make it more complicated for ConstantFolding
later, leading to a higher likelyhood it would have to reject the
expression, even though zero seems like probably the common case here.

Differential Revision: https://reviews.llvm.org/D59730

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 c9839121e7f6..75da481b8c17 100644
--- a/llvm/lib/Transforms/Utils/VNCoercion.cpp
+++ b/llvm/lib/Transforms/Utils/VNCoercion.cpp
@@ -412,12 +412,14 @@ int analyzeLoadFromClobberingMemInst(Type *LoadTy, Value *LoadPtr,
   unsigned AS = Src->getType()->getPointerAddressSpace();
   // Otherwise, see if we can constant fold a load from the constant with the
   // offset applied as appropriate.
-  Src =
-      ConstantExpr::getBitCast(Src, Type::getInt8PtrTy(Src->getContext(), AS));
-  Constant *OffsetCst =
-      ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
-  Src = ConstantExpr::getGetElementPtr(Type::getInt8Ty(Src->getContext()), Src,
-                                       OffsetCst);
+  if (Offset) {
+    Src = ConstantExpr::getBitCast(Src,
+                                   Type::getInt8PtrTy(Src->getContext(), AS));
+    Constant *OffsetCst =
+        ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
+    Src = ConstantExpr::getGetElementPtr(Type::getInt8Ty(Src->getContext()),
+                                         Src, OffsetCst);
+  }
   Src = ConstantExpr::getBitCast(Src, PointerType::get(LoadTy, AS));
   if (ConstantFoldLoadFromConstPtr(Src, LoadTy, DL))
     return Offset;
@@ -587,16 +589,18 @@ T *getMemInstValueForLoadHelper(MemIntrinsic *SrcInst, unsigned Offset,
   // Otherwise, this is a memcpy/memmove from a constant global.
   MemTransferInst *MTI = cast<MemTransferInst>(SrcInst);
   Constant *Src = cast<Constant>(MTI->getSource());
-  unsigned AS = Src->getType()->getPointerAddressSpace();
 
+  unsigned AS = Src->getType()->getPointerAddressSpace();
   // Otherwise, see if we can constant fold a load from the constant with the
   // offset applied as appropriate.
-  Src =
-      ConstantExpr::getBitCast(Src, Type::getInt8PtrTy(Src->getContext(), AS));
-  Constant *OffsetCst =
-      ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
-  Src = ConstantExpr::getGetElementPtr(Type::getInt8Ty(Src->getContext()), Src,
-                                       OffsetCst);
+  if (Offset) {
+    Src = ConstantExpr::getBitCast(Src,
+                                   Type::getInt8PtrTy(Src->getContext(), AS));
+    Constant *OffsetCst =
+        ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
+    Src = ConstantExpr::getGetElementPtr(Type::getInt8Ty(Src->getContext()),
+                                         Src, OffsetCst);
+  }
   Src = ConstantExpr::getBitCast(Src, PointerType::get(LoadTy, AS));
   return ConstantFoldLoadFromConstPtr(Src, LoadTy, DL);
 }