[SelectOpt] Add handling for not conditions. (llvm#92517)

This patch attempts to help the SelectOpt pass detect select groups made
up of conditions and not(conditions). Usually these are canonicalized in
instcombine to remove the not and invert the true/false values, but this
will not happen for Loginal operations, which can be beneficial to
convert if they are part of a larger select group. The handling for
not's are mostly handled in the SelectLike, which can be marked as
Inverted in order to reverse the TrueValue and FalseValue.

This helps fix a regression in fortran minloc constructs, after llvm#84628
helped simplify a loop with branches into a loop with selects.

Author: davemgreen

llvm/lib/CodeGen/SelectOptimize.cpp

@@ -130,7 +130,11 @@ class SelectOptimizeImpl {
   class SelectLike {
     SelectLike(Instruction *I) : I(I) {}
 
+    /// The select (/or) instruction.
     Instruction *I;
+    /// Whether this select is inverted, "not(cond), FalseVal, TrueVal", as
+    /// opposed to the original condition.
+    bool Inverted = false;
 
   public:
     /// Match a select or select-like instruction, returning a SelectLike.
@@ -153,14 +157,22 @@ class SelectOptimizeImpl {
     bool isValid() { return I; }
     operator bool() { return isValid(); }
 
+    /// Invert the select by inverting the condition and switching the operands.
+    void setInverted() {
+      assert(!Inverted && "Trying to invert an inverted SelectLike");
+      assert(isa<Instruction>(getCondition()) &&
+             cast<Instruction>(getCondition())->getOpcode() ==
+                 Instruction::Xor);
+      Inverted = true;
+    }
+    bool isInverted() const { return Inverted; }
+
     Instruction *getI() { return I; }
     const Instruction *getI() const { return I; }
 
     Type *getType() const { return I->getType(); }
 
-    /// Return the condition for the SelectLike instruction. For example the
-    /// condition of a select or c in `or(zext(c), x)`
-    Value *getCondition() const {
+    Value *getNonInvertedCondition() const {
       if (auto *Sel = dyn_cast<SelectInst>(I))
         return Sel->getCondition();
       // Or(zext) case
@@ -177,11 +189,24 @@ class SelectOptimizeImpl {
       llvm_unreachable("Unhandled case in getCondition");
     }
 
+    /// Return the condition for the SelectLike instruction. For example the
+    /// condition of a select or c in `or(zext(c), x)`
+    Value *getCondition() const {
+      Value *CC = getNonInvertedCondition();
+      // For inverted conditions the CC is checked when created to be a not
+      // (xor) instruction.
+      if (Inverted)
+        return cast<Instruction>(CC)->getOperand(0);
+      return CC;
+    }
+
     /// Return the true value for the SelectLike instruction. Note this may not
     /// exist for all SelectLike instructions. For example, for `or(zext(c), x)`
     /// the true value would be `or(x,1)`. As this value does not exist, nullptr
     /// is returned.
-    Value *getTrueValue() const {
+    Value *getTrueValue(bool HonorInverts = true) const {
+      if (Inverted && HonorInverts)
+        return getFalseValue(/*HonorInverts=*/false);
       if (auto *Sel = dyn_cast<SelectInst>(I))
         return Sel->getTrueValue();
       // Or(zext) case - The true value is Or(X), so return nullptr as the value
@@ -195,7 +220,9 @@ class SelectOptimizeImpl {
     /// Return the false value for the SelectLike instruction. For example the
     /// getFalseValue of a select or `x` in `or(zext(c), x)` (which is
     /// `select(c, x|1, x)`)
-    Value *getFalseValue() const {
+    Value *getFalseValue(bool HonorInverts = true) const {
+      if (Inverted && HonorInverts)
+        return getTrueValue(/*HonorInverts=*/false);
       if (auto *Sel = dyn_cast<SelectInst>(I))
         return Sel->getFalseValue();
       // Or(zext) case - return the operand which is not the zext.
@@ -216,8 +243,8 @@ class SelectOptimizeImpl {
     /// InstCostMap. This may need to be generated for select-like instructions.
     Scaled64 getTrueOpCost(DenseMap<const Instruction *, CostInfo> &InstCostMap,
                            const TargetTransformInfo *TTI) {
-      if (auto *Sel = dyn_cast<SelectInst>(I))
-        if (auto *I = dyn_cast<Instruction>(Sel->getTrueValue()))
+      if (isa<SelectInst>(I))
+        if (auto *I = dyn_cast<Instruction>(getTrueValue()))
           return InstCostMap.contains(I) ? InstCostMap[I].NonPredCost
                                          : Scaled64::getZero();
 
@@ -242,8 +269,8 @@ class SelectOptimizeImpl {
     Scaled64
     getFalseOpCost(DenseMap<const Instruction *, CostInfo> &InstCostMap,
                    const TargetTransformInfo *TTI) {
-      if (auto *Sel = dyn_cast<SelectInst>(I))
-        if (auto *I = dyn_cast<Instruction>(Sel->getFalseValue()))
+      if (isa<SelectInst>(I))
+        if (auto *I = dyn_cast<Instruction>(getFalseValue()))
           return InstCostMap.contains(I) ? InstCostMap[I].NonPredCost
                                          : Scaled64::getZero();
 
@@ -510,9 +537,10 @@ getTrueOrFalseValue(SelectOptimizeImpl::SelectLike SI, bool isTrue,
   for (SelectInst *DefSI = dyn_cast<SelectInst>(SI.getI());
        DefSI != nullptr && Selects.count(DefSI);
        DefSI = dyn_cast<SelectInst>(V)) {
-    assert(DefSI->getCondition() == SI.getCondition() &&
-           "The condition of DefSI does not match with SI");
-    V = (isTrue ? DefSI->getTrueValue() : DefSI->getFalseValue());
+    if (DefSI->getCondition() == SI.getCondition())
+      V = (isTrue ? DefSI->getTrueValue() : DefSI->getFalseValue());
+    else // Handle inverted SI
+      V = (!isTrue ? DefSI->getTrueValue() : DefSI->getFalseValue());
   }
 
   if (isa<BinaryOperator>(SI.getI())) {
@@ -632,18 +660,19 @@ void SelectOptimizeImpl::convertProfitableSIGroups(SelectGroups &ProfSIGroups) {
     // Delete the unconditional branch that was just created by the split.
     StartBlock->getTerminator()->eraseFromParent();
 
-    // Move any debug/pseudo instructions that were in-between the select
-    // group to the newly-created end block.
-    SmallVector<Instruction *, 2> DebugPseudoINS;
+    // Move any debug/pseudo instructions and not's that were in-between the
+    // select group to the newly-created end block.
+    SmallVector<Instruction *, 2> SinkInstrs;
     auto DIt = SI.getI()->getIterator();
     while (&*DIt != LastSI.getI()) {
       if (DIt->isDebugOrPseudoInst())
-        DebugPseudoINS.push_back(&*DIt);
+        SinkInstrs.push_back(&*DIt);
+      if (match(&*DIt, m_Not(m_Specific(SI.getCondition()))))
+        SinkInstrs.push_back(&*DIt);
       DIt++;
     }
-    for (auto *DI : DebugPseudoINS) {
+    for (auto *DI : SinkInstrs)
       DI->moveBeforePreserving(&*EndBlock->getFirstInsertionPt());
-    }
 
     // Duplicate implementation for DbgRecords, the non-instruction debug-info
     // format. Helper lambda for moving DbgRecords to the end block.
@@ -765,6 +794,13 @@ void SelectOptimizeImpl::collectSelectGroups(BasicBlock &BB,
           ++BBIt;
           continue;
         }
+
+        // Skip not(select(..)), if the not is part of the same select group
+        if (match(NI, m_Not(m_Specific(SI.getCondition())))) {
+          ++BBIt;
+          continue;
+        }
+
         // We only allow selects in the same group, not other select-like
         // instructions.
         if (!isa<SelectInst>(NI))
@@ -773,6 +809,10 @@ void SelectOptimizeImpl::collectSelectGroups(BasicBlock &BB,
         SelectLike NSI = SelectLike::match(NI);
         if (NSI && SI.getCondition() == NSI.getCondition()) {
           SIGroup.push_back(NSI);
+        } else if (NSI && match(NSI.getCondition(),
+                                m_Not(m_Specific(SI.getCondition())))) {
+          NSI.setInverted();
+          SIGroup.push_back(NSI);
         } else
           break;
         ++BBIt;
@@ -783,6 +823,12 @@ void SelectOptimizeImpl::collectSelectGroups(BasicBlock &BB,
       if (!isSelectKindSupported(SI))
         continue;
 
+      LLVM_DEBUG({
+        dbgs() << "New Select group with\n";
+        for (auto SI : SIGroup)
+          dbgs() << "  " << *SI.getI() << "\n";
+      });
+
       SIGroups.push_back(SIGroup);
     }
   }