[llvm] [SLPVectorizer][X86] Free load cost for stores with constant pointers (PR #118016)

[Antonio Frighetto via llvm-commits]

================
@@ -5157,8 +5157,9 @@ InstructionCost X86TTIImpl::getMemoryOpCost(unsigned Opcode, Type *Src,
 
   InstructionCost Cost = 0;
 
-  // Add a cost for constant load to vector.
-  if (Opcode == Instruction::Store && OpInfo.isConstant())
+  // Add a cost for constant load to vector, if pointer is not a constant.
+  if (auto *SI = dyn_cast_or_null<StoreInst>(I);
+      SI && !isa<Constant>(SI->getPointerOperand()) && OpInfo.isConstant())
----------------
antoniofrighetto wrote:

Sorry, isn't this just bad codegen? In principle, we should be able to simply store the constant in the floating-point register, why would we need to load it from memory? GCC seems to catch this: https://godbolt.org/z/6baWMK4cW. 

https://github.com/llvm/llvm-project/pull/118016