[InstCombine] fold icmp with add/sub instructions having the same operands

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -7728,6 +7728,30 @@ Instruction *InstCombinerImpl::visitICmpInst(ICmpInst &I) {
     }
   }
 
+  // icmp slt (sub nsw x, y), (add nsw x, y)  -->  icmp sgt y, 0
+  // icmp ult (sub nuw x, y), (add nuw x, y)  -->  icmp ugt y, 0
+  // icmp eq (sub nsw/nuw x, y), (add nsw/nuw x, y)   -->  icmp eq y, 0
+  {
+    Value *A, *B;
+    CmpPredicate CmpPred;
+    if (match(&I, m_c_ICmp(CmpPred, m_Sub(m_Value(A), m_Value(B)),
+                           m_c_Add(m_Deferred(A), m_Deferred(B))))) {
+      auto *I0 = cast<OverflowingBinaryOperator>(Op0);
+      auto *I1 = cast<OverflowingBinaryOperator>(Op1);
+      bool I0NUW = I0->hasNoUnsignedWrap();
+      bool I1NUW = I1->hasNoUnsignedWrap();
+      bool I0NSW = I0->hasNoSignedWrap();
+      bool I1NSW = I1->hasNoSignedWrap();
+      if ((ICmpInst::isUnsigned(Pred) && I0NUW && I1NUW) ||
+          (ICmpInst::isSigned(Pred) && I0NSW && I1NSW) ||
+          (ICmpInst::isEquality(Pred) &&
+           ((I0NUW || I0NSW) && (I1NUW || I1NSW)))) {
+        return new ICmpInst(CmpPredicate::getSwapped(CmpPred), B,
+                            ConstantInt::get(Op0->getType(), 0));
+      }
+    }
+  }
+
   // Try to optimize equality comparisons against alloca-based pointers.
   if (Op0->getType()->isPointerTy() && I.isEquality()) {
     assert(Op1->getType()->isPointerTy() &&

llvm/test/Transforms/InstCombine/icmp-subadd.ll

@@ -0,0 +1,111 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+define i1 @test-same-operands-sub-add-nsw-icmp-sgt(i8 %a, i8 %b) {
+; CHECK-LABEL: define i1 @test-same-operands-sub-add-nsw-icmp-sgt(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i8 [[B]], 0
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %sub = sub nsw i8 %a, %b
+  %add = add nsw i8 %a, %b
+  %cmp = icmp sgt i8 %sub, %add
+  ret i1 %cmp
+}
+
+define i1 @test-same-operands-sub-add-nsw-icmp-slt(i8 %a, i8 %b) {
+; CHECK-LABEL: define i1 @test-same-operands-sub-add-nsw-icmp-slt(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i8 [[B]], 0
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %sub = sub nsw i8 %a, %b
+  %add = add nsw i8 %a, %b
+  %cmp = icmp slt i8 %sub, %add
+  ret i1 %cmp
+}
+
+define i1 @test-same-operands-sub-add-nsw-icmp-sle(i8 %a, i8 %b) {
+; CHECK-LABEL: define i1 @test-same-operands-sub-add-nsw-icmp-sle(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i8 [[B]], -1
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %sub = sub nsw i8 %a, %b
+  %add = add nsw i8 %a, %b
+  %cmp = icmp sle i8 %sub, %add
+  ret i1 %cmp
+}
+
+define i1 @test-same-operands-sub-add-nsw-nuw-icmp-eq(i8 %a, i8 %b) {
+; CHECK-LABEL: define i1 @test-same-operands-sub-add-nsw-nuw-icmp-eq(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[B]], 0
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %sub = sub nsw i8 %a, %b
+  %add = add nuw i8 %a, %b
+  %cmp = icmp eq i8 %sub, %add
+  ret i1 %cmp
+}
+
+define i1 @test-same-operands-sub-add-nsw-icmp-eq(i8 %a, i8 %b) {
+; CHECK-LABEL: define i1 @test-same-operands-sub-add-nsw-icmp-eq(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[B]], 0
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %sub = sub nsw i8 %a, %b
+  %add = add nsw i8 %a, %b
+  %cmp = icmp eq i8 %sub, %add
+  ret i1 %cmp
+}
+
+define i1 @test-add-sub-nsw-icmp-sgt(i8 %a, i8 %b) {
+; CHECK-LABEL: define i1 @test-add-sub-nsw-icmp-sgt(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i8 [[B]], 0
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %sub = sub nsw i8 %a, %b
+  %add = add nsw i8 %a, %b
+  %cmp = icmp sgt i8 %add, %sub
+  ret i1 %cmp
+}
+
+define i1 @test-add-sub-nuw-icmp-uge(i8 %a, i8 %b) {
+; CHECK-LABEL: define i1 @test-add-sub-nuw-icmp-uge(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT:    ret i1 true
+;
+  %sub = sub nuw i8 %a, %b
+  %add = add nuw i8 %a, %b
+  %cmp = icmp uge i8 %add, %sub
+  ret i1 %cmp
+}
+
+; Check not folded
+define i1 @test-add-sub-nuw-icmp-sge(i8 %a, i8 %b) {
+; CHECK-LABEL: define i1 @test-add-sub-nuw-icmp-sge(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT:    [[SUB:%.*]] = sub nuw i8 [[A]], [[B]]
+; CHECK-NEXT:    [[ADD:%.*]] = add nuw i8 [[A]], [[B]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sge i8 [[ADD]], [[SUB]]
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %sub = sub nuw i8 %a, %b
+  %add = add nuw i8 %a, %b
+  %cmp = icmp sge i8 %add, %sub
+  ret i1 %cmp
+}
+
+define i1 @test-add-swap-sub-nuw-icmp-uge(i8 %a, i8 %b) {
+; CHECK-LABEL: define i1 @test-add-swap-sub-nuw-icmp-uge(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT:    ret i1 true
+;
+  %sub = sub nuw i8 %a, %b
+  %add = add nuw i8 %b, %a
+  %cmp = icmp uge i8 %add, %sub
+  ret i1 %cmp
+}