[PATCH] D129844: [InstCombine] Relax "(X & 0xFF00) + xx00 --> (X + xx00) & 0xFF00"

[Piotr Sobczak via Phabricator via llvm-commits]

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Add m_OneUse check on X, in addition to the existing one for the AND.

In case the input expression forms part of address computations
(base_addr with offset), the transformation obstructs the original
pattern (base_addr+offset) that could naturally be handled in its
original form by the backends.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D129844

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
@@ -759,6 +759,19 @@
   ret i8 %r
 }
 
+define i8 @masked_add_multi_use(i8 %x) {
+; CHECK-LABEL: @masked_add_multi_use(
+; CHECK-NEXT:    [[AND:%.*]] = and i8 [[X:%.*]], -16
+; CHECK-NEXT:    [[R:%.*]] = add i8 [[AND]], 96
+; CHECK-NEXT:    call void @use(i8 [[X]])
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %and = and i8 %x, -16 ; 0xf0
+  %r = add i8 %and, 96  ; 0x60
+  call void @use(i8 %x) ; extra use
+  ret i8 %r
+}
+
 define i32 @test35(i32 %a) {
 ; CHECK-LABEL: @test35(
 ; CHECK-NEXT:    ret i32 -1
Index: llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -972,7 +972,7 @@
   // If all bits affected by the add are included in a high-bit-mask, do the
   // add before the mask op:
   // (X & 0xFF00) + xx00 --> (X + xx00) & 0xFF00
-  if (match(Op0, m_OneUse(m_And(m_Value(X), m_APInt(C2)))) &&
+  if (match(Op0, m_OneUse(m_And(m_OneUse(m_Value(X)), m_APInt(C2)))) &&
       C2->isNegative() && C2->isShiftedMask() && *C == (*C & *C2)) {
     Value *NewAdd = Builder.CreateAdd(X, ConstantInt::get(Ty, *C));
     return BinaryOperator::CreateAnd(NewAdd, ConstantInt::get(Ty, *C2));


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