Add a pass to lower is.constant and objectsize intrinsics

This pass lowers is.constant and objectsize intrinsics not simplified by
earlier constant folding, i.e. if the object given is not constant or if
not using the optimized pass chain. The result is recursively simplified
and constant conditionals are pruned, so that dead blocks are removed
even for -O0. This allows inline asm blocks with operand constraints to
work all the time.

The new pass replaces the existing lowering in the codegen-prepare pass
and fallbacks in SDAG/GlobalISEL and FastISel. The latter now assert
on the intrinsics.

Differential Revision: https://reviews.llvm.org/D65280

llvm-svn: 374743

1 files changed, 170 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/LowerConstantIntrinsics.cpp b/llvm/lib/Transforms/Scalar/LowerConstantIntrinsics.cpp
new file mode 100644
index 00000000000..d0fcf38b5a7
--- /dev/null
+++ b/llvm/lib/Transforms/Scalar/LowerConstantIntrinsics.cpp
@@ -0,0 +1,170 @@
+//===- LowerConstantIntrinsics.cpp - Lower constant intrinsic calls -------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass lowers all remaining 'objectsize' 'is.constant' intrinsic calls
+// and provides constant propagation and basic CFG cleanup on the result.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Scalar/LowerConstantIntrinsics.h"
+#include "llvm/ADT/PostOrderIterator.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Analysis/MemoryBuiltins.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/PatternMatch.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/Local.h"
+
+using namespace llvm;
+using namespace llvm::PatternMatch;
+
+#define DEBUG_TYPE "lower-is-constant-intrinsic"
+
+STATISTIC(IsConstantIntrinsicsHandled,
+          "Number of 'is.constant' intrinsic calls handled");
+STATISTIC(ObjectSizeIntrinsicsHandled,
+          "Number of 'objectsize' intrinsic calls handled");
+
+static Value *lowerIsConstantIntrinsic(IntrinsicInst *II) {
+  Value *Op = II->getOperand(0);
+
+  return isa<Constant>(Op) ? ConstantInt::getTrue(II->getType())
+                           : ConstantInt::getFalse(II->getType());
+}
+
+static bool replaceConditionalBranchesOnConstant(Instruction *II,
+                                                 Value *NewValue) {
+  bool HasDeadBlocks = false;
+  SmallSetVector<Instruction *, 8> Worklist;
+  replaceAndRecursivelySimplify(II, NewValue, nullptr, nullptr, nullptr,
+                                &Worklist);
+  for (auto I : Worklist) {
+    BranchInst *BI = dyn_cast<BranchInst>(I);
+    if (!BI)
+      continue;
+    if (BI->isUnconditional())
+      continue;
+
+    BasicBlock *Target, *Other;
+    if (match(BI->getOperand(0), m_Zero())) {
+      Target = BI->getSuccessor(1);
+      Other = BI->getSuccessor(0);
+    } else if (match(BI->getOperand(0), m_One())) {
+      Target = BI->getSuccessor(0);
+      Other = BI->getSuccessor(1);
+    } else {
+      Target = nullptr;
+      Other = nullptr;
+    }
+    if (Target && Target != Other) {
+      BasicBlock *Source = BI->getParent();
+      Other->removePredecessor(Source);
+      BI->eraseFromParent();
+      BranchInst::Create(Target, Source);
+      if (pred_begin(Other) == pred_end(Other))
+        HasDeadBlocks = true;
+    }
+  }
+  return HasDeadBlocks;
+}
+
+static bool lowerConstantIntrinsics(Function &F, const TargetLibraryInfo *TLI) {
+  bool HasDeadBlocks = false;
+  const auto &DL = F.getParent()->getDataLayout();
+  SmallVector<WeakTrackingVH, 8> Worklist;
+
+  ReversePostOrderTraversal<Function *> RPOT(&F);
+  for (BasicBlock *BB : RPOT) {
+    for (Instruction &I: *BB) {
+      IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I);
+      if (!II)
+        continue;
+      switch (II->getIntrinsicID()) {
+      default:
+        break;
+      case Intrinsic::is_constant:
+      case Intrinsic::objectsize:
+        Worklist.push_back(WeakTrackingVH(&I));
+        break;
+      }
+    }
+  }
+  for (WeakTrackingVH &VH: Worklist) {
+    // Items on the worklist can be mutated by earlier recursive replaces.
+    // This can remove the intrinsic as dead (VH == null), but also replace
+    // the intrinsic in place.
+    if (!VH)
+      continue;
+    IntrinsicInst *II = dyn_cast<IntrinsicInst>(&*VH);
+    if (!II)
+      continue;
+    Value *NewValue;
+    switch (II->getIntrinsicID()) {
+    default:
+      continue;
+    case Intrinsic::is_constant:
+      NewValue = lowerIsConstantIntrinsic(II);
+      IsConstantIntrinsicsHandled++;
+      break;
+    case Intrinsic::objectsize:
+      NewValue = lowerObjectSizeCall(II, DL, TLI, true);
+      ObjectSizeIntrinsicsHandled++;
+      break;
+    }
+    HasDeadBlocks |= replaceConditionalBranchesOnConstant(II, NewValue);
+  }
+  if (HasDeadBlocks)
+    removeUnreachableBlocks(F);
+  return !Worklist.empty();
+}
+
+PreservedAnalyses
+LowerConstantIntrinsicsPass::run(Function &F, FunctionAnalysisManager &AM) {
+  if (lowerConstantIntrinsics(F, AM.getCachedResult<TargetLibraryAnalysis>(F)))
+    return PreservedAnalyses::none();
+
+  return PreservedAnalyses::all();
+}
+
+namespace {
+/// Legacy pass for lowering is.constant intrinsics out of the IR.
+///
+/// When this pass is run over a function it converts is.constant intrinsics
+/// into 'true' or 'false'. This is completements the normal constand folding
+/// to 'true' as part of Instruction Simplify passes.
+class LowerConstantIntrinsics : public FunctionPass {
+public:
+  static char ID;
+  LowerConstantIntrinsics() : FunctionPass(ID) {
+    initializeLowerConstantIntrinsicsPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnFunction(Function &F) override {
+    auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
+    const TargetLibraryInfo *TLI = TLIP ? &TLIP->getTLI(F) : nullptr;
+    return lowerConstantIntrinsics(F, TLI);
+  }
+};
+} // namespace
+
+char LowerConstantIntrinsics::ID = 0;
+INITIALIZE_PASS(LowerConstantIntrinsics, "lower-constant-intrinsics",
+                "Lower constant intrinsics", false, false)
+
+FunctionPass *llvm::createLowerConstantIntrinsicsPass() {
+  return new LowerConstantIntrinsics();
+}