Rip min/max pattern matching out of InstCombine and into

 ValueTracking.

This matching functionality is useful in more than just InstCombine, so
make it available in ValueTracking.

NFC.

llvm-svn: 236998

1 files changed, 81 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 8eb2e68bc48..3ad7c7af651 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -3204,3 +3204,84 @@ OverflowResult llvm::computeOverflowForUnsignedAdd(Value *LHS, Value *RHS,
 
   return OverflowResult::MayOverflow;
 }
+
+SelectPatternFlavor llvm::matchSelectPattern(Value *V,
+                                             Value *&LHS, Value *&RHS) {
+  SelectInst *SI = dyn_cast<SelectInst>(V);
+  if (!SI) return SPF_UNKNOWN;
+
+  ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition());
+  if (!ICI) return SPF_UNKNOWN;
+
+  ICmpInst::Predicate Pred = ICI->getPredicate();
+  Value *CmpLHS = ICI->getOperand(0);
+  Value *CmpRHS = ICI->getOperand(1);
+  Value *TrueVal = SI->getTrueValue();
+  Value *FalseVal = SI->getFalseValue();
+
+  LHS = CmpLHS;
+  RHS = CmpRHS;
+
+  // (icmp X, Y) ? X : Y
+  if (TrueVal == CmpLHS && FalseVal == CmpRHS) {
+    switch (Pred) {
+    default: return SPF_UNKNOWN; // Equality.
+    case ICmpInst::ICMP_UGT:
+    case ICmpInst::ICMP_UGE: return SPF_UMAX;
+    case ICmpInst::ICMP_SGT:
+    case ICmpInst::ICMP_SGE: return SPF_SMAX;
+    case ICmpInst::ICMP_ULT:
+    case ICmpInst::ICMP_ULE: return SPF_UMIN;
+    case ICmpInst::ICMP_SLT:
+    case ICmpInst::ICMP_SLE: return SPF_SMIN;
+    }
+  }
+
+  // (icmp X, Y) ? Y : X
+  if (TrueVal == CmpRHS && FalseVal == CmpLHS) {
+    switch (Pred) {
+    default: return SPF_UNKNOWN; // Equality.
+    case ICmpInst::ICMP_UGT:
+    case ICmpInst::ICMP_UGE: return SPF_UMIN;
+    case ICmpInst::ICMP_SGT:
+    case ICmpInst::ICMP_SGE: return SPF_SMIN;
+    case ICmpInst::ICMP_ULT:
+    case ICmpInst::ICMP_ULE: return SPF_UMAX;
+    case ICmpInst::ICMP_SLT:
+    case ICmpInst::ICMP_SLE: return SPF_SMAX;
+    }
+  }
+
+  if (ConstantInt *C1 = dyn_cast<ConstantInt>(CmpRHS)) {
+    if ((CmpLHS == TrueVal && match(FalseVal, m_Neg(m_Specific(CmpLHS)))) ||
+        (CmpLHS == FalseVal && match(TrueVal, m_Neg(m_Specific(CmpLHS))))) {
+
+      // ABS(X) ==> (X >s 0) ? X : -X and (X >s -1) ? X : -X
+      // NABS(X) ==> (X >s 0) ? -X : X and (X >s -1) ? -X : X
+      if (Pred == ICmpInst::ICMP_SGT && (C1->isZero() || C1->isMinusOne())) {
+        return (CmpLHS == TrueVal) ? SPF_ABS : SPF_NABS;
+      }
+
+      // ABS(X) ==> (X <s 0) ? -X : X and (X <s 1) ? -X : X
+      // NABS(X) ==> (X <s 0) ? X : -X and (X <s 1) ? X : -X
+      if (Pred == ICmpInst::ICMP_SLT && (C1->isZero() || C1->isOne())) {
+        return (CmpLHS == FalseVal) ? SPF_ABS : SPF_NABS;
+      }
+    }
+    
+    // Y >s C ? ~Y : ~C == ~Y <s ~C ? ~Y : ~C = SMIN(~Y, ~C)
+    if (const auto *C2 = dyn_cast<ConstantInt>(FalseVal)) {
+      if (C1->getType() == C2->getType() && ~C1->getValue() == C2->getValue() &&
+          (match(TrueVal, m_Not(m_Specific(CmpLHS))) ||
+           match(CmpLHS, m_Not(m_Specific(TrueVal))))) {
+        LHS = TrueVal;
+        RHS = FalseVal;
+        return SPF_SMIN;
+      }
+    }
+  }
+
+  // TODO: (X > 4) ? X : 5   -->  (X >= 5) ? X : 5  -->  MAX(X, 5)
+
+  return SPF_UNKNOWN;
+}