Index: lib/Transforms/InstCombine/InstCombine.h
===================================================================
--- lib/Transforms/InstCombine/InstCombine.h
+++ lib/Transforms/InstCombine/InstCombine.h
@@ -35,8 +35,8 @@
 enum SelectPatternFlavor {
   SPF_UNKNOWN = 0,
   SPF_SMIN, SPF_UMIN,
-  SPF_SMAX, SPF_UMAX
-  //SPF_ABS - TODO.
+  SPF_SMAX, SPF_UMAX,
+  SPF_ABS
 };
 
 /// getComplexity:  Assign a complexity or rank value to LLVM Values...
Index: lib/Transforms/InstCombine/InstCombineSelect.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -31,13 +31,18 @@
   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 +56,30 @@
   }
 
   // (icmp X, Y) ? Y : X
-  if (SI->getTrueValue() == ICI->getOperand(1) &&
-      SI->getFalseValue() == ICI->getOperand(0)) {
-    switch (ICI->getPredicate()) {
-      default: return SPF_UNKNOWN; // Equality.
+  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;
+    }
+  }
+
+  // (X > -1) ? X : -X
+  if (ConstantInt *C1 = dyn_cast<ConstantInt>(CmpRHS)) {
+    if (C1->isMinusOne() && CmpLHS == TrueVal &&
+        (match(TrueVal, m_Neg(m_Specific(FalseVal))) ||
+         match(FalseVal, m_Neg(m_Specific(TrueVal))))) {
+      switch (Pred) {
+      default: return SPF_UNKNOWN;
       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;
+      case ICmpInst::ICMP_SGT: return SPF_ABS;
+      }
     }
   }
 
@@ -71,7 +88,6 @@
   return SPF_UNKNOWN;
 }
 
-
 /// GetSelectFoldableOperands - We want to turn code that looks like this:
 ///   %C = or %A, %B
 ///   %D = select %cond, %C, %A
@@ -652,6 +668,11 @@
   }
 
   // TODO: MIN(MIN(A, 23), 97)
+
+  // ABS(ABS(X)) -> ABS(X)
+  if (SPF1 == SPF_ABS && SPF2 == SPF_ABS)
+    return ReplaceInstUsesWith(Outer, Inner);
+
   return nullptr;
 }
 
@@ -957,7 +978,6 @@
 
     // 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.
Index: test/Transforms/InstCombine/select.ll
===================================================================
--- test/Transforms/InstCombine/select.ll
+++ test/Transforms/InstCombine/select.ll
@@ -1031,3 +1031,17 @@
 ; CHECK: lshr exact i32 %2, 1
 ; CHECK: xor i32 %3, 42
 }
+
+; ABS(ABS(X)) -> ABS(X)
+define i32 @abs(i32 %x) {
+entry:
+  %sub = sub nsw i32 0, %x
+  %ispos = icmp sgt i32 %sub, -1
+  %0 = select i1 %ispos, i32 %sub, i32 %x
+  %ispos2 = icmp sgt i32 %0, -1
+  %neg3 = sub i32 0, %0
+  %1 = select i1 %ispos2, i32 %0, i32 %neg3
+  ret i32 %1
+; CHECK-LABEL: @abs(
+; CHECK: ret i32 %0
+}
\ No newline at end of file