Added select flavour for ABS and NEG(ABS)

This patch can identify 
  ABS(X) ==> (X >s 0) ? X : -X and (X >s -1) ? X : -X
  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
  NABS(X) ==> (X <s 0) ? X : -X and (X <s 1) ? X : -X
  
and can transform
  ABS(ABS(X)) -> ABS(X)
  NABS(NABS(X)) -> NABS(X)
  
Differential Revision: http://reviews.llvm.org/D3658

llvm-svn: 210312

2 files changed, 51 insertions, 20 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombine.h b/llvm/lib/Transforms/InstCombine/InstCombine.h
index e04b1be53df..ea1839c3bcf 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombine.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombine.h
@@ -37,8 +37,9 @@ enum SelectPatternFlavor {
   SPF_SMIN,
   SPF_UMIN,
   SPF_SMAX,
-  SPF_UMAX
-  // SPF_ABS - TODO.
+  SPF_UMAX,
+  SPF_ABS,
+  SPF_NABS
 };
 
 /// getComplexity:  Assign a complexity or rank value to LLVM Values...
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index caf9e6af7d4..e8ce350886d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -31,13 +31,18 @@ MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) {
   ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition());
   if (!ICI) return SPF_UNKNOWN;
 
-  LHS = ICI->getOperand(0);
-  RHS = ICI->getOperand(1);
+  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 (SI->getTrueValue() == ICI->getOperand(0) &&
-      SI->getFalseValue() == ICI->getOperand(1)) {
-    switch (ICI->getPredicate()) {
+  if (TrueVal == CmpLHS && FalseVal == CmpRHS) {
+    switch (Pred) {
     default: return SPF_UNKNOWN; // Equality.
     case ICmpInst::ICMP_UGT:
     case ICmpInst::ICMP_UGE: return SPF_UMAX;
@@ -51,18 +56,35 @@ MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) {
   }
 
   // (icmp X, Y) ? Y : X
-  if (SI->getTrueValue() == ICI->getOperand(1) &&
-      SI->getFalseValue() == ICI->getOperand(0)) {
-    switch (ICI->getPredicate()) {
-      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 (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;
+      }
     }
   }
 
@@ -704,6 +726,15 @@ Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner,
       }
     }
   }
+
+  // ABS(ABS(X)) -> ABS(X)
+  // NABS(NABS(X)) -> NABS(X)
+  if (SPF1 == SPF2 && (SPF1 == SPF_ABS || SPF1 == SPF_NABS)) {
+    return ReplaceInstUsesWith(Outer, Inner);
+  }
+
+  // TODO: ABS(NABS(X)) -> ABS(X)
+  // TODO: NABS(ABS(X)) -> NABS(X)
   return nullptr;
 }
 
@@ -1008,7 +1039,6 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
 
     // TODO.
     // ABS(-X) -> ABS(X)
-    // ABS(ABS(X)) -> ABS(X)
   }
 
   // See if we can fold the select into a phi node if the condition is a select.