[llvm] [DirectX] Start the creation of a DXIL Instruction legalizer (PR #131221)

[Justin Bogner via llvm-commits]

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@@ -0,0 +1,209 @@
+//===- DXILLegalizePass.cpp - Legalizes llvm IR for DXIL ------------------===//
+//
+// 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
+//
+//===---------------------------------------------------------------------===//
+//===---------------------------------------------------------------------===//
+///
+/// \file This file contains a pass to remove i8 truncations and i64 extract
+/// and insert elements.
+///
+//===----------------------------------------------------------------------===//
+#include "DXILLegalizePass.h"
+#include "DirectX.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/Pass.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include <functional>
+#include <map>
+#include <stack>
+#include <vector>
+
+#define DEBUG_TYPE "dxil-legalize"
+
+using namespace llvm;
+namespace {
+
+static void fixI8TruncUseChain(Instruction &I,
+                               std::stack<Instruction *> &ToRemove,
+                               std::map<Value *, Value *> &ReplacedValues) {
+
+  auto *Cmp = dyn_cast<CmpInst>(&I);
+
+  if (auto *Trunc = dyn_cast<TruncInst>(&I)) {
+    if (Trunc->getDestTy()->isIntegerTy(8)) {
+      ReplacedValues[Trunc] = Trunc->getOperand(0);
+      ToRemove.push(Trunc);
+    }
+  } else if (I.getType()->isIntegerTy(8) ||
+             (Cmp && Cmp->getOperand(0)->getType()->isIntegerTy(8))) {
+    IRBuilder<> Builder(&I);
+
+    std::vector<Value *> NewOperands;
+    Type *InstrType = IntegerType::get(I.getContext(), 32);
+    for (unsigned OpIdx = 0; OpIdx < I.getNumOperands(); ++OpIdx) {
+      Value *Op = I.getOperand(OpIdx);
+      if (ReplacedValues.count(Op))
+        InstrType = ReplacedValues[Op]->getType();
+    }
+    for (unsigned OpIdx = 0; OpIdx < I.getNumOperands(); ++OpIdx) {
+      Value *Op = I.getOperand(OpIdx);
+      if (ReplacedValues.count(Op))
+        NewOperands.push_back(ReplacedValues[Op]);
+      else if (auto *Imm = dyn_cast<ConstantInt>(Op)) {
+        APInt Value = Imm->getValue();
+        unsigned NewBitWidth = InstrType->getIntegerBitWidth();
+        // Note: options here are sext or sextOrTrunc.
+        // Since i8 isn't supported, we assume new values
+        // will always have a higher bitness.
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bogner wrote:

An assert to document/enforce the assumption wouldn't hurt

https://github.com/llvm/llvm-project/pull/131221