Index: lib/Transforms/InstCombine/InstCombineSelect.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -362,6 +362,22 @@
   return Builder->CreateOr(V, Y);
 }
 
+static Value *foldSelectICmpAndSub(SelectInst &SI, Value *TrueVal,
+                                   Value *FalseVal,
+                                   InstCombiner::BuilderTy *Builder) {
+  const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
+  Value *CmpLHS = IC->getOperand(0);
+  Value *CmpRHS = IC->getOperand(1);
+
+  if (match(FalseVal, m_Sub(m_Value(CmpLHS), m_Value(CmpRHS))) &&
+      match(TrueVal, m_Zero())) {
+    Value *A = Builder->CreateSelect(SI.getCondition(), CmpRHS, CmpLHS);
+    return Builder->CreateSub(A, CmpRHS);
+  }
+
+  return nullptr;
+}
+
 /// Attempt to fold a cttz/ctlz followed by a icmp plus select into a single
 /// call to cttz/ctlz with flag 'is_zero_undef' cleared.
 ///
@@ -667,6 +683,9 @@
   if (Value *V = foldSelectICmpAndOr(SI, TrueVal, FalseVal, Builder))
     return replaceInstUsesWith(SI, V);
 
+  if (Value *V = foldSelectICmpAndSub(SI, TrueVal, FalseVal, Builder))
+    return replaceInstUsesWith(SI, V);
+
   if (Value *V = foldSelectCttzCtlz(ICI, TrueVal, FalseVal, Builder))
     return replaceInstUsesWith(SI, V);