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      1 //===-- RelLookupTableConverterPass.h - Rel Table Conv ----------*- C++ -*-===//
      2 //
      3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
      4 // See https://llvm.org/LICENSE.txt for license information.
      5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
      6 //
      7 //===----------------------------------------------------------------------===//
      8 //
      9 /// \file
     10 /// This file implements relative lookup table converter that converts
     11 /// lookup tables to relative lookup tables to make them PIC-friendly.
     12 ///
     13 /// Switch lookup table example:
     14 /// @switch.table.foo = private unnamed_addr constant [3 x i8*]
     15 /// [
     16 /// i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0),
     17 /// i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.1, i64 0, i64 0),
     18 /// i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.2, i64 0, i64 0)
     19 /// ], align 8
     20 ///
     21 /// switch.lookup:
     22 ///   %1 = sext i32 %cond to i64
     23 ///   %switch.gep = getelementptr inbounds [3 x i8*],
     24 ///                 [3 x i8*]* @switch.table.foo, i64 0, i64 %1
     25 ///   %switch.load = load i8*, i8** %switch.gep, align 8
     26 ///  ret i8* %switch.load
     27 ///
     28 /// Switch lookup table will become a relative lookup table that
     29 /// consists of relative offsets.
     30 ///
     31 /// @reltable.foo = private unnamed_addr constant [3 x i32]
     32 /// [
     33 /// i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str to i64),
     34 ///                     i64 ptrtoint ([3 x i32]* @reltable.foo to i64)) to i32),
     35 /// i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.1 to i64),
     36 ///                     i64 ptrtoint ([3 x i32]* @reltable.foo to i64)) to i32),
     37 /// i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.2 to i64),
     38 ///                     i64 ptrtoint ([3 x i32]* @reltable.foo to i64)) to i32)
     39 /// ], align 4
     40 ///
     41 /// IR after converting to a relative lookup table:
     42 /// switch.lookup:
     43 ///  %1 = sext i32 %cond to i64
     44 ///  %reltable.shift = shl i64 %1, 2
     45 ///  %reltable.intrinsic = call i8* @llvm.load.relative.i64(
     46 ///                        i8* bitcast ([3 x i32]* @reltable.foo to i8*),
     47 ///                        i64 %reltable.shift)
     48 ///  ret i8* %reltable.intrinsic
     49 //===----------------------------------------------------------------------===//
     50 
     51 #ifndef LLVM_TRANSFORMS_UTILS_RELLOOKUPTABLECONVERTER_H
     52 #define LLVM_TRANSFORMS_UTILS_RELLOOKUPTABLECONVERTER_H
     53 
     54 #include "llvm/IR/Module.h"
     55 #include "llvm/IR/PassManager.h"
     56 
     57 namespace llvm {
     58 
     59 // Pass that converts lookup tables to relative lookup tables.
     60 class RelLookupTableConverterPass
     61     : public PassInfoMixin<RelLookupTableConverterPass> {
     62 public:
     63   RelLookupTableConverterPass() = default;
     64 
     65   PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM);
     66 };
     67 
     68 } // end namespace llvm
     69 
     70 #endif // LLVM_TRANSFORMS_UTILS_RELLOOKUPTABLECONVERTER_H
     71