1 files changed, 28 insertions, 17 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 3ee418feb0e..9fb77abad66 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -680,25 +680,46 @@ static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal,
   if (!Cmp->hasOneUse())
     return nullptr;
 
-  // Canonicalize to 'ULT' to simplify matching below.
   Value *Cmp0 = Cmp->getOperand(0);
   Value *Cmp1 = Cmp->getOperand(1);
+
+  // Match unsigned saturated add with constant.
+  Value *X;
+  const APInt *C, *CmpC;
+  if (match(TVal, m_Add(m_Value(X), m_APInt(C))) && X == Cmp0 &&
+      match(Cmp1, m_APInt(CmpC)) && *CmpC == ~*C) {
+    // Commute compare predicate and select operands. The backend is expecting
+    // this form (-1 is true value). If this changes, the backend must be
+    // updated too:
+    // (X u< ~C) ? (X + C) : -1 --> (X u> ~C) ? -1 : (X + C)
+    Value *NewCmp = Builder.CreateICmp(ICmpInst::ICMP_UGT, X, Cmp1);
+    return Builder.CreateSelect(NewCmp, FVal, TVal);
+  }
+
+  // Match unsigned saturated add of 2 variables with an unnecessary 'not'.
+  // There are 8 commuted variants.
+  // Canonicalize -1 (saturated result) to true value of the select.
+  if (match(FVal, m_AllOnes())) {
+    std::swap(TVal, FVal);
+    std::swap(Cmp0, Cmp1);
+  }
+  if (!match(TVal, m_AllOnes()))
+    return nullptr;
+
+  // Canonicalize predicate to 'ULT'.
   ICmpInst::Predicate Pred = Cmp->getPredicate();
   if (Pred == ICmpInst::ICMP_UGT) {
     Pred = ICmpInst::ICMP_ULT;
     std::swap(Cmp0, Cmp1);
   }
-
   if (Pred != ICmpInst::ICMP_ULT)
     return nullptr;
 
-  // Match unsigned saturated add of 2 variables with an unnecessary 'not'.
-  // TODO: There are more variations of this pattern.
-  Value *X, *Y;
-  if (match(TVal, m_AllOnes()) && match(Cmp0, m_Not(m_Value(X))) &&
+  Value *Y;
+  if (match(Cmp0, m_Not(m_Value(X))) &&
       match(FVal, m_c_Add(m_Specific(X), m_Value(Y))) && Y == Cmp1) {
     // Change the comparison to use the sum (false value of the select). That is
-    // the canonical pattern match form for uadd.with.overflow and eliminates a
+    // a canonical pattern match form for uadd.with.overflow and eliminates a
     // use of the 'not' op:
     // (~X u< Y) ? -1 : (X + Y) --> ((X + Y) u< Y) ? -1 : (X + Y)
     // (~X u< Y) ? -1 : (Y + X) --> ((Y + X) u< Y) ? -1 : (Y + X)
@@ -706,16 +727,6 @@ static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal,
     return Builder.CreateSelect(NewCmp, TVal, FVal);
   }
 
-  // Match unsigned saturated add with constant.
-  const APInt *C, *CmpC;
-  if (match(TVal, m_Add(m_Value(X), m_APInt(C))) && X == Cmp0 &&
-      match(FVal, m_AllOnes()) && match(Cmp1, m_APInt(CmpC)) && *CmpC == ~*C) {
-    // Commute compare predicate and select operands:
-    // (X u< ~C) ? (X + C) : -1 --> (X u> ~C) ? -1 : (X + C)
-    Value *NewCmp = Builder.CreateICmp(ICmpInst::ICMP_UGT, X, Cmp1);
-    return Builder.CreateSelect(NewCmp, FVal, TVal);
-  }
-
   return nullptr;
 }