[InstCombine] Remove one-use requirement for add iN (sext i1 X), (sext i1 Y) --> sext (X | Y) to iN

Since these remove instructions, we can forgo the one-use check, as long as at least ONE of the two sexts are one-use.

Author: AZero13

llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp

@@ -510,10 +510,10 @@ Value *InstCombinerImpl::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
       }
 
       // add iN (sext i1 X), (sext i1 Y) --> sext (X | Y) to iN
-      // TODO: Relax the one-use checks because we are removing an instruction?
-      if (match(I, m_Add(m_OneUse(m_SExt(m_Value(X))),
-                         m_OneUse(m_SExt(m_Value(Y))))) &&
-          X->getType()->isIntOrIntVectorTy(1) && X->getType() == Y->getType()) {
+      if (match(I, m_Add(m_SExt(m_Value(X)), m_SExt(m_Value(Y)))) &&
+          X->getType()->isIntOrIntVectorTy(1) && X->getType() == Y->getType() &&
+          (I->getOperand(0)->hasOneUse() || I->getOperand(1)->hasOneUse())) {
+
         // Truth table for inputs and output signbits:
         //       X:0 | X:1
         //      -----------

llvm/test/Transforms/InstCombine/add.ll

@@ -1437,11 +1437,10 @@ define i32 @and31_add_sexts(i1 %x, i1 %y) {
 
 define i32 @lshr_add_use_sexts(i1 %x, i1 %y, ptr %p) {
 ; CHECK-LABEL: @lshr_add_use_sexts(
-; CHECK-NEXT:    [[XS:%.*]] = sext i1 [[X:%.*]] to i32
 ; CHECK-NEXT:    [[YS:%.*]] = sext i1 [[Y:%.*]] to i32
 ; CHECK-NEXT:    store i32 [[YS]], ptr [[P:%.*]], align 4
-; CHECK-NEXT:    [[SUB:%.*]] = add nsw i32 [[XS]], [[YS]]
-; CHECK-NEXT:    [[R:%.*]] = lshr i32 [[SUB]], 31
+; CHECK-NEXT:    [[TMP1:%.*]] = or i1 [[X:%.*]], [[Y]]
+; CHECK-NEXT:    [[R:%.*]] = zext i1 [[TMP1]] to i32
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %xs = sext i1 %x to i32
@@ -1456,9 +1455,8 @@ define i32 @lshr_add_use_sexts_2(i1 %x, i1 %y, ptr %p) {
 ; CHECK-LABEL: @lshr_add_use_sexts_2(
 ; CHECK-NEXT:    [[XS:%.*]] = sext i1 [[X:%.*]] to i32
 ; CHECK-NEXT:    store i32 [[XS]], ptr [[P:%.*]], align 4
-; CHECK-NEXT:    [[YS:%.*]] = sext i1 [[Y:%.*]] to i32
-; CHECK-NEXT:    [[SUB:%.*]] = add nsw i32 [[XS]], [[YS]]
-; CHECK-NEXT:    [[R:%.*]] = lshr i32 [[SUB]], 31
+; CHECK-NEXT:    [[TMP1:%.*]] = or i1 [[X]], [[Y:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = zext i1 [[TMP1]] to i32
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %xs = sext i1 %x to i32