[llvm] [llvm][ARM]Add widen strings pass (PR #107120)

[Nashe Mncube via llvm-commits]

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@@ -2029,6 +2031,109 @@ OptimizeFunctions(Module &M,
   return Changed;
 }
 
+static bool IsCharArray(Type *T) {
+  const unsigned int CHAR_BIT_SIZE = 8;
+  return T && T->isArrayTy() && T->getArrayElementType()->isIntegerTy() &&
+         T->getArrayElementType()->getIntegerBitWidth() == CHAR_BIT_SIZE;
+}
+
+static bool tryWidenGlobalString(CallInst *CI, GlobalVariable *SourceVar,
+                                 unsigned NumBytesToPad,
+                                 unsigned NumBytesToCopy,
+                                 ConstantInt *BytesToCopyOp) {
+  auto *F = CI->getCalledFunction();
+  auto *Alloca = dyn_cast<AllocaInst>(CI->getArgOperand(0));
+  auto *IsVolatile = dyn_cast<ConstantInt>(CI->getArgOperand(3));
+
+  if (!Alloca || !IsVolatile || IsVolatile->isOne())
+    return false;
+
+  if (!SourceVar->hasInitializer() || !SourceVar->isConstant() ||
+      !SourceVar->hasLocalLinkage() || !SourceVar->hasGlobalUnnamedAddr())
+    return false;
+
+  if (!Alloca->isStaticAlloca() || !IsCharArray(Alloca->getAllocatedType()))
+    return false;
+
+  ConstantDataArray *SourceDataArray =
+      dyn_cast<ConstantDataArray>(SourceVar->getInitializer());
+  if (!SourceDataArray || !IsCharArray(SourceDataArray->getType()))
+    return false;
+
+  uint64_t DZSize = Alloca->getAllocatedType()->getArrayNumElements();
+  uint64_t SZSize = SourceDataArray->getType()->getNumElements();
+
+  // For safety purposes lets add a constraint and only pad when
+  // num bytes to copy == destination array size == source string
+  // which is a constant
+  if (NumBytesToCopy != DZSize || DZSize != SZSize)
+    return false;
+
+  unsigned int TotalBytes = NumBytesToCopy + NumBytesToPad;
+
+  // Update destination char array to be word aligned (memcpy(X,...,...))
+  IRBuilder<> BuildAlloca(Alloca);
+  AllocaInst *NewAlloca = BuildAlloca.CreateAlloca(ArrayType::get(
+      Alloca->getAllocatedType()->getArrayElementType(), TotalBytes));
+  NewAlloca->takeName(Alloca);
+  NewAlloca->setAlignment(Alloca->getAlign());
+  Alloca->replaceAllUsesWith(NewAlloca);
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nasherm wrote:

Done

https://github.com/llvm/llvm-project/pull/107120