2 files changed, 98 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index fa4432ea23e..2185848cbdc 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -222,6 +222,10 @@ static cl::opt<bool>
                          cl::init(true),
                          cl::desc("Enable splitting large offset of GEP."));
 
+static cl::opt<bool> EnableICMP_EQToICMP_ST(
+    "cgp-icmp-eq2icmp-st", cl::Hidden, cl::init(false),
+    cl::desc("Enable ICMP_EQ to ICMP_S(L|G)T conversion."));
+
 namespace {
 
 enum ExtType {
@@ -1408,6 +1412,93 @@ static bool sinkCmpExpression(CmpInst *Cmp, const TargetLowering &TLI) {
   return MadeChange;
 }
 
+/// For pattern like:
+///
+///   DomCond = icmp sgt/slt CmpOp0, CmpOp1 (might not be in DomBB)
+///   ...
+/// DomBB:
+///   ...
+///   br DomCond, TrueBB, CmpBB
+/// CmpBB: (with DomBB being the single predecessor)
+///   ...
+///   Cmp = icmp eq CmpOp0, CmpOp1
+///   ...
+///
+/// It would use two comparison on targets that lowering of icmp sgt/slt is
+/// different from lowering of icmp eq (PowerPC). This function try to convert
+/// 'Cmp = icmp eq CmpOp0, CmpOp1' to ' Cmp = icmp slt/sgt CmpOp0, CmpOp1'.
+/// After that, DomCond and Cmp can use the same comparison so reduce one
+/// comparison.
+///
+/// Return true if any changes are made.
+static bool foldICmpWithDominatingICmp(CmpInst *Cmp,
+                                       const TargetLowering &TLI) {
+  if (!EnableICMP_EQToICMP_ST && TLI.isEqualityCmpFoldedWithSignedCmp())
+    return false;
+
+  ICmpInst::Predicate Pred = Cmp->getPredicate();
+  if (Pred != ICmpInst::ICMP_EQ)
+    return false;
+
+  // If icmp eq has users other than BranchInst and SelectInst, converting it to
+  // icmp slt/sgt would introduce more redundant LLVM IR.
+  for (User *U : Cmp->users()) {
+    if (isa<BranchInst>(U))
+      continue;
+    if (isa<SelectInst>(U) && cast<SelectInst>(U)->getCondition() == Cmp)
+      continue;
+    return false;
+  }
+
+  // This is a cheap/incomplete check for dominance - just match a single
+  // predecessor with a conditional branch.
+  BasicBlock *CmpBB = Cmp->getParent();
+  BasicBlock *DomBB = CmpBB->getSinglePredecessor();
+  if (!DomBB)
+    return false;
+
+  // We want to ensure that the only way control gets to the comparison of
+  // interest is that a less/greater than comparison on the same operands is
+  // false.
+  Value *DomCond;
+  BasicBlock *TrueBB, *FalseBB;
+  if (!match(DomBB->getTerminator(), m_Br(m_Value(DomCond), TrueBB, FalseBB)))
+    return false;
+  if (CmpBB != FalseBB)
+    return false;
+
+  Value *CmpOp0 = Cmp->getOperand(0), *CmpOp1 = Cmp->getOperand(1);
+  ICmpInst::Predicate DomPred;
+  if (!match(DomCond, m_ICmp(DomPred, m_Specific(CmpOp0), m_Specific(CmpOp1))))
+    return false;
+  if (DomPred != ICmpInst::ICMP_SGT && DomPred != ICmpInst::ICMP_SLT)
+    return false;
+
+  // Convert the equality comparison to the opposite of the dominating
+  // comparison and swap the direction for all branch/select users.
+  // We have conceptually converted:
+  // Res = (a < b) ? <LT_RES> : (a == b) ? <EQ_RES> : <GT_RES>;
+  // to
+  // Res = (a < b) ? <LT_RES> : (a > b)  ? <GT_RES> : <EQ_RES>;
+  // And similarly for branches.
+  for (User *U : Cmp->users()) {
+    if (auto *BI = dyn_cast<BranchInst>(U)) {
+      assert(BI->isConditional() && "Must be conditional");
+      BI->swapSuccessors();
+      continue;
+    }
+    if (auto *SI = dyn_cast<SelectInst>(U)) {
+      // Swap operands
+      SI->swapValues();
+      SI->swapProfMetadata();
+      continue;
+    }
+    llvm_unreachable("Must be a branch or a select");
+  }
+  Cmp->setPredicate(CmpInst::getSwappedPredicate(DomPred));
+  return true;
+}
+
 bool CodeGenPrepare::optimizeCmp(CmpInst *Cmp, bool &ModifiedDT) {
   if (sinkCmpExpression(Cmp, *TLI))
     return true;
@@ -1418,6 +1509,9 @@ bool CodeGenPrepare::optimizeCmp(CmpInst *Cmp, bool &ModifiedDT) {
   if (combineToUSubWithOverflow(Cmp, ModifiedDT))
     return true;
 
+  if (foldICmpWithDominatingICmp(Cmp, *TLI))
+    return true;
+
   return false;
 }
 
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.h b/llvm/lib/Target/PowerPC/PPCISelLowering.h
index 7016a601490..a01134321b9 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.h
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.h
@@ -650,6 +650,10 @@ namespace llvm {
       return true;
     }
 
+    bool isEqualityCmpFoldedWithSignedCmp() const override {
+      return false;
+    }
+
     bool hasAndNotCompare(SDValue) const override {
       return true;
     }