[InstCombine] re-commit r218721 with fix for pr21199

The icmp-select-icmp optimization targets select-icmp.eq
only. This is now ensured by testing the branch predicate
explictly. This commit also includes the test case for pr21199.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219282 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/InstCombine/InstCombine.h

@@ -14,6 +14,7 @@
 #include "llvm/Analysis/AssumptionTracker.h"
 #include "llvm/Analysis/TargetFolder.h"
 #include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/Dominators.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/InstVisitor.h"
 #include "llvm/IR/IntrinsicInst.h"
@@ -98,7 +99,7 @@ class LLVM_LIBRARY_VISIBILITY InstCombiner
   AssumptionTracker *AT;
   const DataLayout *DL;
   TargetLibraryInfo *TLI;
-  DominatorTree *DT; // not required
+  DominatorTree *DT;
   bool MadeIRChange;
   LibCallSimplifier *Simplifier;
   bool MinimizeSize;
@@ -113,7 +114,8 @@ public:
   BuilderTy *Builder;
 
   static char ID; // Pass identification, replacement for typeid
-  InstCombiner() : FunctionPass(ID), DL(nullptr), Builder(nullptr) {
+  InstCombiner()
+      : FunctionPass(ID), DL(nullptr), DT(nullptr), Builder(nullptr) {
     MinimizeSize = false;
     initializeInstCombinerPass(*PassRegistry::getPassRegistry());
   }
@@ -242,6 +244,11 @@ public:
 
   // visitInstruction - Specify what to return for unhandled instructions...
   Instruction *visitInstruction(Instruction &I) { return nullptr; }
+  bool dominatesAllUses(const Instruction *DI, const Instruction *UI,
+                        const BasicBlock *DB) const;
+  bool replacedSelectWithOperand(SelectInst *SI, const ICmpInst *Icmp,
+                                 const ConstantInt *CI1,
+                                 const ConstantInt *CI2);
 
 private:
   bool ShouldChangeType(Type *From, Type *To) const;

lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -2429,6 +2429,125 @@ static bool swapMayExposeCSEOpportunities(const Value * Op0,
   return GlobalSwapBenefits > 0;
 }
 
+/// \brief Check that one use is in the same block as the definition and all
+/// other uses are in blocks dominated by a given block
+///
+/// \param DI Definition
+/// \param UI Use
+/// \param DB Block that must dominate all uses of \p DI outside
+///           the parent block
+/// \return true when \p UI is the only use of \p DI in the parent block
+/// and all other uses of \p DI are in blocks dominated by \p DB.
+///
+bool InstCombiner::dominatesAllUses(const Instruction *DI,
+                                    const Instruction *UI,
+                                    const BasicBlock *DB) const {
+  assert(DI && UI && "Instruction not defined\n");
+  if (DI->getParent() != UI->getParent())
+    return false;
+  // DominatorTree available?
+  if (!DT)
+    return false;
+  for (const User *U : DI->users()) {
+    auto *Usr = cast<Instruction>(U);
+    if (Usr != UI && !DT->dominates(DB, Usr->getParent()))
+      return false;
+  }
+  return true;
+}
+
+///
+/// true when the instruction sequence within a block is select-cmp-br.
+///
+static bool isChainSelectCmpBranch(const SelectInst *SI) {
+  const BasicBlock *BB = SI->getParent();
+  if (!BB)
+    return false;
+  auto *BI = dyn_cast_or_null<BranchInst>(BB->getTerminator());
+  if (!BI || BI->getNumSuccessors() != 2)
+    return false;
+  auto *IC = dyn_cast<ICmpInst>(BI->getCondition());
+  if (!IC || (IC->getOperand(0) != SI && IC->getOperand(1) != SI))
+    return false;
+  return true;
+}
+
+///
+/// \brief True when a select result is replaced by one of its operands
+/// in select-icmp sequence. This will eventually result in the elimination
+/// of the select.
+///
+/// \param SI   Select instruction
+/// \param Icmp Compare instruction
+/// \param CI1  'true' when first select operand is equal to RHSC of Icmp
+/// \param CI2  'true' when second select operand is equal to RHSC of Icmp
+///
+/// Notes:
+/// - The replacement is global and requires dominator information
+/// - The caller is responsible for the actual replacement
+///
+/// Example:
+///
+/// entry:
+///  %4 = select i1 %3, %C* %0, %C* null
+///  %5 = icmp eq %C* %4, null
+///  br i1 %5, label %9, label %7
+///  ...
+///  ; <label>:7                                       ; preds = %entry
+///  %8 = getelementptr inbounds %C* %4, i64 0, i32 0
+///  ...
+///
+/// can be transformed to
+///
+///  %5 = icmp eq %C* %0, null
+///  %6 = select i1 %3, i1 %5, i1 true
+///  br i1 %6, label %9, label %7
+///  ...
+///  ; <label>:7                                       ; preds = %entry
+///  %8 = getelementptr inbounds %C* %0, i64 0, i32 0  // replace by %0!
+///
+/// Similar when the first operand of the select is a constant or/and
+/// the compare is for not equal rather than equal.
+///
+/// FIXME: Currently the function considers equal compares only. It should be
+/// possbile to extend it to not equal compares also.
+///
+bool InstCombiner::replacedSelectWithOperand(SelectInst *SI,
+                                             const ICmpInst *Icmp,
+                                             const ConstantInt *CI1,
+                                             const ConstantInt *CI2) {
+  if (isChainSelectCmpBranch(SI) &&
+      Icmp->getPredicate() == ICmpInst::ICMP_EQ) {
+    // Code sequence is select - icmp.eq - br
+    unsigned ReplaceWithOpd = 0;
+    if (CI1 && !CI1->isZero())
+      // The first constant operand of the select and the RHS of
+      // the compare match, so try to substitute
+      // the select results with its second operand
+      // Example:
+      // %4 = select i1 %3, %C* null, %C* %0
+      // %5 = icmp eq %C* %4, null
+      // ==> could replace select with second operand
+      ReplaceWithOpd = 2;
+    else if (CI2 && !CI2->isZero())
+      // Similar when the second operand of the select is a constant
+      // Example:
+      // %4 = select i1 %3, %C* %0, %C* null
+      // %5 = icmp eq %C* %4, null
+      // ==> could replace select with first operand
+      ReplaceWithOpd = 1;
+    if (ReplaceWithOpd) {
+      // Replace select with operand on else path for EQ compares.
+      BasicBlock *Succ = SI->getParent()->getTerminator()->getSuccessor(1);
+      if (InstCombiner::dominatesAllUses(SI, Icmp, Succ)) {
+        SI->replaceAllUsesWith(SI->getOperand(ReplaceWithOpd));
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
 Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
   bool Changed = false;
   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
@@ -2885,8 +3004,21 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
         // fold to a constant (in which case the icmp is replaced with a select
         // which will usually simplify) or this is the only user of the
         // select (in which case we are trading a select+icmp for a simpler
-        // select+icmp).
-        if ((Op1 && Op2) || (LHSI->hasOneUse() && (Op1 || Op2))) {
+        // select+icmp) or all uses of the select can be replaced based on
+        // dominance information ("Global cases").
+        bool Transform = false;
+        if (Op1 && Op2)
+          Transform = true;
+        else if (Op1 || Op2) {
+          if (LHSI->hasOneUse())
+            Transform = true;
+          else
+            // Global cases
+            Transform = replacedSelectWithOperand(
+                cast<SelectInst>(LHSI), &I, dyn_cast_or_null<ConstantInt>(Op1),
+                dyn_cast_or_null<ConstantInt>(Op2));
+        }
+        if (Transform) {
           if (!Op1)
             Op1 = Builder->CreateICmp(I.getPredicate(), LHSI->getOperand(1),
                                       RHSC, I.getName());

lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -90,6 +90,7 @@ INITIALIZE_PASS_BEGIN(InstCombiner, "instcombine",
                 "Combine redundant instructions", false, false)
 INITIALIZE_PASS_DEPENDENCY(AssumptionTracker)
 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 INITIALIZE_PASS_END(InstCombiner, "instcombine",
                 "Combine redundant instructions", false, false)
 
@@ -97,6 +98,8 @@ void InstCombiner::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.setPreservesCFG();
   AU.addRequired<AssumptionTracker>();
   AU.addRequired<TargetLibraryInfo>();
+  AU.addRequired<DominatorTreeWrapperPass>();
+  AU.addPreserved<DominatorTreeWrapperPass>();
 }
 
 
@@ -2933,12 +2936,9 @@ bool InstCombiner::runOnFunction(Function &F) {
   AT = &getAnalysis<AssumptionTracker>();
   DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
   DL = DLP ? &DLP->getDataLayout() : nullptr;
+  DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
   TLI = &getAnalysis<TargetLibraryInfo>();
 
-  DominatorTreeWrapperPass *DTWP =
-      getAnalysisIfAvailable<DominatorTreeWrapperPass>();
-  DT = DTWP ? &DTWP->getDomTree() : nullptr;
-
   // Minimizing size?
   MinimizeSize = F.getAttributes().hasAttribute(AttributeSet::FunctionIndex,
                                                 Attribute::MinSize);

test/Transforms/InstCombine/pr12338.ll

@@ -2,11 +2,11 @@
 
 define void @entry() nounwind {
 entry:
+; CHECK: br label %for.cond
   br label %for.cond
 
 for.cond:
   %local = phi <1 x i32> [ <i32 0>, %entry ], [ %phi2, %cond.end47 ]
-; CHECK: sub <1 x i32> <i32 92>, %local
   %phi3 = sub <1 x i32> zeroinitializer, %local
   br label %cond.end
 

test/Transforms/InstCombine/pr21199.ll

@@ -0,0 +1,25 @@
+; do not replace a 'select' with 'or' in 'select - cmp - br' sequence
+; RUN: opt -instcombine -S < %s | FileCheck %s
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+declare void @f(i32)
+
+define void @test(i32 %len) {
+entry:
+  %cmp = icmp ult i32 %len, 8
+  %cond = select i1 %cmp, i32 %len, i32 8
+  %cmp11 = icmp ult i32 0, %cond
+  br i1 %cmp11, label %for.body, label %for.end
+
+for.body:                                         ; preds = %entry, %for.body
+  %i.02 = phi i32 [ %inc, %for.body ], [ 0, %entry ]
+  tail call void @f(i32 %cond)
+  %inc = add i32 %i.02, 1
+  %cmp1 = icmp ult i32 %inc, %cond
+  br i1 %cmp1, label %for.body, label %for.end
+
+for.end:                                          ; preds = %for.body, %entry
+  ret void
+; CHECK: select
+}

test/Transforms/InstCombine/select-cmp-br.ll

@@ -0,0 +1,127 @@
+; Replace a 'select' with 'or' in 'select - cmp [eq|ne] - br' sequence
+; RUN: opt -instcombine -S < %s | FileCheck %s
+
+%C = type <{ %struct.S }>
+%struct.S = type { i64*, i32, i32 }
+
+declare void @bar(%struct.S *) #1
+
+define void @test1(%C*) {
+entry:
+  %1 = getelementptr inbounds %C* %0, i64 0, i32 0, i32 0
+  %m = load i64** %1, align 8
+  %2 = getelementptr inbounds %C* %0, i64 1, i32 0, i32 0
+  %n = load i64** %2, align 8
+  %3 = getelementptr inbounds i64* %m, i64 9
+  %4 = bitcast i64* %3 to i64 (%C*)**
+  %5 = load i64 (%C*)** %4, align 8
+  %6 = icmp eq i64* %m, %n
+  %7 = select i1 %6, %C* %0, %C* null
+  %8 = icmp eq %C* %7, null
+  br i1 %8, label %12, label %10
+
+; <label>:9                                       ; preds = %10, %12
+  ret void
+
+; <label>:10                                      ; preds = %entry
+  %11 = getelementptr inbounds %C* %7, i64 0, i32 0
+  tail call void @bar(%struct.S* %11)
+  br label %9
+
+; <label>:12                                      ; preds = %entry
+  %13 = tail call i64 %5(%C* %0)
+  br label %9
+; CHECK-LABEL: @test1(
+; CHECK-NOT: select
+; CHECK: or
+}
+
+define void @test2(%C*) {
+entry:
+  %1 = getelementptr inbounds %C* %0, i64 0, i32 0, i32 0
+  %m = load i64** %1, align 8
+  %2 = getelementptr inbounds %C* %0, i64 1, i32 0, i32 0
+  %n = load i64** %2, align 8
+  %3 = getelementptr inbounds i64* %m, i64 9
+  %4 = bitcast i64* %3 to i64 (%C*)**
+  %5 = load i64 (%C*)** %4, align 8
+  %6 = icmp eq i64* %m, %n
+  %7 = select i1 %6, %C* null, %C* %0
+  %8 = icmp eq %C* %7, null
+  br i1 %8, label %12, label %10
+
+; <label>:9                                       ; preds = %10, %12
+  ret void
+
+; <label>:10                                      ; preds = %entry
+  %11 = getelementptr inbounds %C* %7, i64 0, i32 0
+  tail call void @bar(%struct.S* %11)
+  br label %9
+
+; <label>:12                                      ; preds = %entry
+  %13 = tail call i64 %5(%C* %0)
+  br label %9
+; CHECK-LABEL: @test2(
+; CHECK-NOT: select
+; CHECK: or
+}
+
+define void @test3(%C*) {
+entry:
+  %1 = getelementptr inbounds %C* %0, i64 0, i32 0, i32 0
+  %m = load i64** %1, align 8
+  %2 = getelementptr inbounds %C* %0, i64 1, i32 0, i32 0
+  %n = load i64** %2, align 8
+  %3 = getelementptr inbounds i64* %m, i64 9
+  %4 = bitcast i64* %3 to i64 (%C*)**
+  %5 = load i64 (%C*)** %4, align 8
+  %6 = icmp eq i64* %m, %n
+  %7 = select i1 %6, %C* %0, %C* null
+  %8 = icmp ne %C* %7, null
+  br i1 %8, label %10, label %12
+
+; <label>:9                                       ; preds = %10, %12
+  ret void
+
+; <label>:10                                      ; preds = %entry
+  %11 = getelementptr inbounds %C* %7, i64 0, i32 0
+  tail call void @bar(%struct.S* %11)
+  br label %9
+
+; <label>:12                                      ; preds = %entry
+  %13 = tail call i64 %5(%C* %0)
+  br label %9
+; CHECK-LABEL: @test3(
+; CHECK-NOT: select
+; CHECK: or
+}
+
+define void @test4(%C*) {
+entry:
+  %1 = getelementptr inbounds %C* %0, i64 0, i32 0, i32 0
+  %m = load i64** %1, align 8
+  %2 = getelementptr inbounds %C* %0, i64 1, i32 0, i32 0
+  %n = load i64** %2, align 8
+  %3 = getelementptr inbounds i64* %m, i64 9
+  %4 = bitcast i64* %3 to i64 (%C*)**
+  %5 = load i64 (%C*)** %4, align 8
+  %6 = icmp eq i64* %m, %n
+  %7 = select i1 %6, %C* null, %C* %0
+  %8 = icmp ne %C* %7, null
+  br i1 %8, label %10, label %12
+
+; <label>:9                                       ; preds = %10, %12
+  ret void
+
+; <label>:10                                      ; preds = %entry
+  %11 = getelementptr inbounds %C* %7, i64 0, i32 0
+  tail call void @bar(%struct.S* %11)
+  br label %9
+
+; <label>:12                                      ; preds = %entry
+  %13 = tail call i64 %5(%C* %0)
+  br label %9
+; CHECK-LABEL: @test4(
+; CHECK-NOT: select
+; CHECK: or
+}