[InstCombine] Remove one-use check if other logic operand is constant (#77973)

By using `match(W, m_ImmConstant())`, we do not need to worry about
one-time use anymore.

Author: AZero13

llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp

@@ -366,14 +366,14 @@ static Instruction *foldShiftOfShiftedBinOp(BinaryOperator &I,
 
   Type *Ty = I.getType();
 
-  // Find a matching one-use shift by constant. The fold is not valid if the sum
+  // Find a matching shift by constant. The fold is not valid if the sum
   // of the shift values equals or exceeds bitwidth.
-  // TODO: Remove the one-use check if the other logic operand (Y) is constant.
   Value *X, *Y;
-  auto matchFirstShift = [&](Value *V) {
-    APInt Threshold(Ty->getScalarSizeInBits(), Ty->getScalarSizeInBits());
-    return match(V,
-                 m_OneUse(m_BinOp(ShiftOpcode, m_Value(X), m_Constant(C0)))) &&
+  auto matchFirstShift = [&](Value *V, Value *W) {
+    unsigned Size = Ty->getScalarSizeInBits();
+    APInt Threshold(Size, Size);
+    return match(V, m_BinOp(ShiftOpcode, m_Value(X), m_Constant(C0))) &&
+           (V->hasOneUse() || match(W, m_ImmConstant())) &&
            match(ConstantExpr::getAdd(C0, C1),
                  m_SpecificInt_ICMP(ICmpInst::ICMP_ULT, Threshold));
   };
@@ -382,9 +382,9 @@ static Instruction *foldShiftOfShiftedBinOp(BinaryOperator &I,
   // is not so we cannot reoder if we match operand(1) and need to keep the
   // operands in their original positions.
   bool FirstShiftIsOp1 = false;
-  if (matchFirstShift(BinInst->getOperand(0)))
+  if (matchFirstShift(BinInst->getOperand(0), BinInst->getOperand(1)))
     Y = BinInst->getOperand(1);
-  else if (matchFirstShift(BinInst->getOperand(1))) {
+  else if (matchFirstShift(BinInst->getOperand(1), BinInst->getOperand(0))) {
     Y = BinInst->getOperand(0);
     FirstShiftIsOp1 = BinInst->getOpcode() == Instruction::Sub;
   } else

llvm/test/Transforms/InstCombine/shift-logic.ll

@@ -346,6 +346,36 @@ define i8 @shl_add(i8 %x, i8 %y) {
   ret i8 %sh1
 }
 
+define i8 @shl_add_multiuse(i8 %x) {
+; CHECK-LABEL: @shl_add_multiuse(
+; CHECK-NEXT:    [[SH0:%.*]] = shl i8 [[X:%.*]], 3
+; CHECK-NEXT:    call void @use(i8 [[SH0]])
+; CHECK-NEXT:    [[R:%.*]] = shl i8 [[X]], 5
+; CHECK-NEXT:    [[SH1:%.*]] = add i8 [[R]], 88
+; CHECK-NEXT:    ret i8 [[SH1]]
+;
+  %sh0 = shl i8 %x, 3
+  %r = add i8 %sh0, -42
+  call void @use(i8 %sh0)
+  %sh1 = shl i8 %r, 2
+  ret i8 %sh1
+}
+
+define i8 @shl_add_multiuse_nonconstant(i8 %x, i8 %y) {
+; CHECK-LABEL: @shl_add_multiuse_nonconstant(
+; CHECK-NEXT:    [[SH0:%.*]] = shl i8 [[X:%.*]], 3
+; CHECK-NEXT:    [[R:%.*]] = add i8 [[SH0]], [[Y:%.*]]
+; CHECK-NEXT:    call void @use(i8 [[SH0]])
+; CHECK-NEXT:    [[SH1:%.*]] = shl i8 [[R]], 2
+; CHECK-NEXT:    ret i8 [[SH1]]
+;
+  %sh0 = shl i8 %x, 3
+  %r = add i8 %sh0, %y
+  call void @use(i8 %sh0)
+  %sh1 = shl i8 %r, 2
+  ret i8 %sh1
+}
+
 define <2 x i8> @shl_add_nonuniform(<2 x i8> %x, <2 x i8> %y) {
 ; CHECK-LABEL: @shl_add_nonuniform(
 ; CHECK-NEXT:    [[TMP1:%.*]] = shl <2 x i8> [[X:%.*]], <i8 5, i8 4>