[ConstraintElim] Decompose sub nsw

Author: dtcxzyw

llvm/lib/Transforms/Scalar/ConstraintElimination.cpp

@@ -522,6 +522,13 @@ static Decomposition decompose(Value *V,
     if (match(V, m_NSWAdd(m_Value(Op0), m_Value(Op1))))
       return MergeResults(Op0, Op1, IsSigned);
 
+    if (match(V, m_NSWSub(m_Value(Op0), m_Value(Op1)))) {
+      auto ResA = decompose(Op0, Preconditions, IsSigned, DL);
+      auto ResB = decompose(Op1, Preconditions, IsSigned, DL);
+      ResA.sub(ResB);
+      return ResA;
+    }
+
     ConstantInt *CI;
     if (match(V, m_NSWMul(m_Value(Op0), m_ConstantInt(CI))) && canUseSExt(CI)) {
       auto Result = decompose(Op0, Preconditions, IsSigned, DL);

llvm/test/Transforms/ConstraintElimination/sub-nsw.ll

@@ -9,8 +9,7 @@ define i1 @test_decompose_sub_nsw_sgt_nonneg(i32 %x, i32 %y) {
 ; CHECK-NEXT:    [[COND:%.*]] = icmp sgt i32 [[SUB]], 10
 ; CHECK-NEXT:    br i1 [[COND]], label %[[IF_THEN:.*]], label %[[IF_ELSE:.*]]
 ; CHECK:       [[IF_THEN]]:
-; CHECK-NEXT:    [[RET:%.*]] = icmp slt i32 [[X]], [[Y]]
-; CHECK-NEXT:    ret i1 [[RET]]
+; CHECK-NEXT:    ret i1 true
 ; CHECK:       [[IF_ELSE]]:
 ; CHECK-NEXT:    ret i1 true
 ;
@@ -35,8 +34,7 @@ define i1 @test_decompose_sub_nsw_sgt_zero(i32 %x, i32 %y) {
 ; CHECK-NEXT:    [[COND:%.*]] = icmp sgt i32 [[SUB]], 0
 ; CHECK-NEXT:    br i1 [[COND]], label %[[IF_THEN:.*]], label %[[IF_ELSE:.*]]
 ; CHECK:       [[IF_THEN]]:
-; CHECK-NEXT:    [[RET:%.*]] = icmp slt i32 [[X]], [[Y]]
-; CHECK-NEXT:    ret i1 [[RET]]
+; CHECK-NEXT:    ret i1 true
 ; CHECK:       [[IF_ELSE]]:
 ; CHECK-NEXT:    ret i1 true
 ;
@@ -61,8 +59,7 @@ define i1 @test_decompose_sub_nsw_sgt_zero_inv(i32 %x, i32 %y) {
 ; CHECK-NEXT:    [[COND:%.*]] = icmp sgt i32 [[SUB]], 10
 ; CHECK-NEXT:    br i1 [[COND]], label %[[IF_THEN:.*]], label %[[IF_ELSE:.*]]
 ; CHECK:       [[IF_THEN]]:
-; CHECK-NEXT:    [[RET:%.*]] = icmp sge i32 [[X]], [[Y]]
-; CHECK-NEXT:    ret i1 [[RET]]
+; CHECK-NEXT:    ret i1 false
 ; CHECK:       [[IF_ELSE]]:
 ; CHECK-NEXT:    ret i1 true
 ;