[PATCH] D149471: [InstCombine] Add A - B + B << 1 --> A + B

[Ryan Taylor via Phabricator via llvm-commits]

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Add instcombine transform A - B + B << 1 --> A + B


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D149471

Files:
  llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
  llvm/test/Transforms/InstCombine/add.ll


Index: llvm/test/Transforms/InstCombine/add.ll
===================================================================
--- llvm/test/Transforms/InstCombine/add.ll
+++ llvm/test/Transforms/InstCombine/add.ll
@@ -2943,4 +2943,14 @@
   ret <2 x i32> %c
 }
 
+define i32 @add_shl_sub(i32 %a, i32 %b) {
+; CHECK-LABEL: @add_shl_sub
+; CHECK-NEXT: %add = add i32 %a, %b
+; CHECK-NEXT: ret i32 %add
+  %sub = sub i32 %a, %b
+  %mul = shl nsw i32 %b, 1
+  %add = add nsw i32 %sub, %mul
+  ret i32 %add
+}
+
 declare void @llvm.assume(i1)
Index: llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1390,6 +1390,13 @@
   }
 
   Value *A, *B;
+
+  // A - B + B << 1 -> A + B
+  if (match(LHS, m_Sub(m_Value(A), m_Value(B))) &&
+      match(RHS, m_Shl(m_Value(B), m_One())) &&
+      LHS->hasOneUse() && RHS->hasOneUse())
+    return BinaryOperator::CreateAdd(A, B);
+
   if (match(LHS, m_Neg(m_Value(A)))) {
     // -A + -B --> -(A + B)
     if (match(RHS, m_Neg(m_Value(B))))


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