[clang] [llvm] [DXIL] `exp`, `any`, `lerp`, & `rcp` Intrinsic Lowering (PR #84526)

[Farzon Lotfi via cfe-commits]

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@@ -0,0 +1,186 @@
+//===- DXILIntrinsicExpansion.cpp - Prepare LLVM Module for DXIL encoding--===//
+//
+// 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 DXIL intrinsic expansions for those that don't have
+//  opcodes in DirectX Intermediate Language (DXIL).
+//===----------------------------------------------------------------------===//
+
+#include "DXILIntrinsicExpansion.h"
+#include "DirectX.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/IntrinsicsDirectX.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/PassManager.h"
+#include "llvm/IR/Type.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/MathExtras.h"
+
+#define DEBUG_TYPE "dxil-intrinsic-expansion"
+
+using namespace llvm;
+
+static bool isIntrinsicExpansion(Function &F) {
+  switch (F.getIntrinsicID()) {
+  case Intrinsic::exp:
+  case Intrinsic::dx_any:
+  case Intrinsic::dx_lerp:
+  case Intrinsic::dx_rcp:
+    return true;
+  }
+  return false;
+}
+
+static bool expandExpIntrinsic(CallInst *Orig) {
+  Value *X = Orig->getOperand(0);
+  IRBuilder<> Builder(Orig->getParent());
+  Builder.SetInsertPoint(Orig);
+  Type *Ty = X->getType();
+  Type *EltTy = Ty->getScalarType();
+  Constant *Log2eConst =
+      Ty->isVectorTy() ? ConstantVector::getSplat(
+                             ElementCount::getFixed(
+                                 cast<FixedVectorType>(Ty)->getNumElements()),
+                             ConstantFP::get(EltTy, numbers::log2e))
+                       : ConstantFP::get(EltTy, numbers::log2e);
+  Value *NewX = Builder.CreateFMul(Log2eConst, X);
+  auto *Exp2Call =
+      Builder.CreateIntrinsic(Ty, Intrinsic::exp2, {NewX}, nullptr, "dx.exp2");
+  Exp2Call->setTailCall(Orig->isTailCall());
+  Exp2Call->setAttributes(Orig->getAttributes());
+  Orig->replaceAllUsesWith(Exp2Call);
+  Orig->eraseFromParent();
+  return true;
+}
+
+static bool expandAnyIntrinsic(CallInst *Orig) {
+  Value *X = Orig->getOperand(0);
+  IRBuilder<> Builder(Orig->getParent());
+  Builder.SetInsertPoint(Orig);
+  Type *Ty = X->getType();
+  Type *EltTy = Ty->getScalarType();
+
+  if (!Ty->isVectorTy()) {
+    Value *Cond = EltTy->isFloatingPointTy()
+                      ? Builder.CreateFCmpUNE(X, ConstantFP::get(EltTy, 0))
+                      : Builder.CreateICmpNE(X, ConstantInt::get(EltTy, 0));
+    Orig->replaceAllUsesWith(Cond);
+  } else {
+    auto *XVec = dyn_cast<FixedVectorType>(Ty);
+    Value *Cond =
+        EltTy->isFloatingPointTy()
+            ? Builder.CreateFCmpUNE(
+                  X, ConstantVector::getSplat(
+                         ElementCount::getFixed(XVec->getNumElements()),
+                         ConstantFP::get(EltTy, 0)))
+            : Builder.CreateICmpNE(
+                  X, ConstantVector::getSplat(
+                         ElementCount::getFixed(XVec->getNumElements()),
+                         ConstantInt::get(EltTy, 0)));
+    Value *Result = Builder.CreateExtractElement(Cond, (uint64_t)0);
+    for (unsigned I = 1; I < XVec->getNumElements(); I++) {
+      Value *Elt = Builder.CreateExtractElement(Cond, I);
+      Result = Builder.CreateOr(Result, Elt);
+    }
+    Orig->replaceAllUsesWith(Result);
+  }
+  Orig->eraseFromParent();
+  return true;
+}
+
+static bool expandLerpIntrinsic(CallInst *Orig) {
+  Value *X = Orig->getOperand(0);
+  Value *Y = Orig->getOperand(1);
+  Value *S = Orig->getOperand(2);
+  IRBuilder<> Builder(Orig->getParent());
+  Builder.SetInsertPoint(Orig);
+  auto *V = Builder.CreateFSub(Y, X);
+  V = Builder.CreateFMul(S, V);
+  auto *Result = Builder.CreateFAdd(X, V, "dx.lerp");
+  Orig->replaceAllUsesWith(Result);
+  Orig->eraseFromParent();
+  return true;
+}
+
+static bool expandRcpIntrinsic(CallInst *Orig) {
+  Value *X = Orig->getOperand(0);
+  IRBuilder<> Builder(Orig->getParent());
+  Builder.SetInsertPoint(Orig);
+  Type *Ty = X->getType();
+  Type *EltTy = Ty->getScalarType();
+  Constant *One =
+      Ty->isVectorTy()
+          ? ConstantVector::getSplat(
+                ElementCount::getFixed(
+                    dyn_cast<FixedVectorType>(Ty)->getNumElements()),
+                ConstantFP::get(EltTy, 1.0))
+          : ConstantFP::get(EltTy, 1.0);
+  auto *Result = Builder.CreateFDiv(One, X, "dx.rcp");
+  Orig->replaceAllUsesWith(Result);
+  Orig->eraseFromParent();
+  return true;
+}
+
+static bool expandIntrinsic(Function &F, CallInst *Orig) {
+  switch (F.getIntrinsicID()) {
+  case Intrinsic::exp:
+    return expandExpIntrinsic(Orig);
+  case Intrinsic::dx_any:
+    return expandAnyIntrinsic(Orig);
+  case Intrinsic::dx_lerp:
+    return expandLerpIntrinsic(Orig);
+  case Intrinsic::dx_rcp:
+    return expandRcpIntrinsic(Orig);
+  }
+  return false;
+}
+
+static bool expansionIntrinsics(Module &M) {
+  for (auto &F : make_early_inc_range(M.functions())) {
+    if (!isIntrinsicExpansion(F))
+      continue;
+    bool IntrinsicExpanded = false;
+    for (User *U : make_early_inc_range(F.users())) {
+      auto *IntrinsicCall = dyn_cast<CallInst>(U);
+      if (!IntrinsicCall)
+        continue;
+      IntrinsicExpanded = expandIntrinsic(F, IntrinsicCall);
----------------
farzonl wrote:

No if the intrinsic isn't found in the switch statement, then we return false and thus there will not be an `F.eraseFromParent()`.  This is just a last cleanup step. we do an  `Orig->eraseFromParent();`  on the `CallInst`. But if uses on the Function are not empty we want to cleanup here as well. 

https://github.com/llvm/llvm-project/pull/84526