[llvm] Add a pass to convert jump tables to switches. (PR #77709)

[Nikita Popov via llvm-commits]

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@@ -0,0 +1,194 @@
+//===- JumpTableToSwitch.cpp ----------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Scalar/JumpTableToSwitch.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/Analysis/ConstantFolding.h"
+#include "llvm/Analysis/DomTreeUpdater.h"
+#include "llvm/Analysis/PostDominators.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/PatternMatch.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/Cloning.h"
+#include "llvm/Transforms/Utils/Local.h"
+
+using namespace llvm;
+using namespace PatternMatch;
+
+static cl::opt<unsigned>
+    JumpTableSizeThreshold("jump-table-to-switch-size-threshold", cl::Hidden,
+                           cl::desc("Only split jump tables with size less or "
+                                    "equal than JumpTableSizeThreshold."),
+                           cl::init(10));
+
+#define DEBUG_TYPE "jump-table-to-switch"
+
+namespace {
+struct JumpTableTy {
+  Value *Index;
+  SmallVector<Function *, 5> Funcs;
+};
+} // anonymous namespace
+
+static std::optional<JumpTableTy> parseJumpTable(GetElementPtrInst *GEP) {
+  if (!GEP || !GEP->isInBounds())
+    return std::nullopt;
+  ArrayType *ArrayTy = dyn_cast<ArrayType>(GEP->getSourceElementType());
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nikic wrote:

Do not check GEP source element type. Please add a test where the GEP operates on a `{ [N x ptr ] }` global, which is (iirc) how this would look like in rust.

https://github.com/llvm/llvm-project/pull/77709