[SCCP] Extend visitBinaryOperator to overflowing binary ops

Leverage more refined ranges results when handling overflowing
binary operators.

Author: antoniofrighetto

llvm/lib/Transforms/Utils/SCCPSolver.cpp

@@ -1486,7 +1486,13 @@ void SCCPInstVisitor::visitBinaryOperator(Instruction &I) {
   // Try to simplify to a constant range.
   ConstantRange A = getConstantRange(V1State, I.getType());
   ConstantRange B = getConstantRange(V2State, I.getType());
-  ConstantRange R = A.binaryOp(cast<BinaryOperator>(&I)->getOpcode(), B);
+
+  auto *BO = cast<BinaryOperator>(&I);
+  ConstantRange R = ConstantRange::getEmpty(I.getType()->getScalarSizeInBits());
+  if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(BO))
+    R = A.overflowingBinaryOp(BO->getOpcode(), B, OBO->getNoWrapKind());
+  else
+    R = A.binaryOp(BO->getOpcode(), B);
   mergeInValue(&I, ValueLatticeElement::getRange(R));
 
   // TODO: Currently we do not exploit special values that produce something

llvm/test/Transforms/SCCP/add-nuw-nsw-flags.ll

@@ -240,3 +240,32 @@ then:
 else:
   ret i16 0
 }
+
+define i1 @test_add_nuw_sub(i32 %a) {
+; CHECK-LABEL: @test_add_nuw_sub(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[ADD:%.*]] = add nuw i32 [[A:%.*]], 10000
+; CHECK-NEXT:    [[SUB:%.*]] = add i32 [[ADD]], -5000
+; CHECK-NEXT:    ret i1 false
+;
+entry:
+  %add = add nuw i32 %a, 10000
+  %sub = add i32 %add, -5000
+  %cond = icmp ult i32 %sub, 5000
+  ret i1 %cond
+}
+
+define i1 @test_add_nsw_sub(i32 %a) {
+; CHECK-LABEL: @test_add_nsw_sub(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[ADD:%.*]] = add nsw i32 [[A:%.*]], 10000
+; CHECK-NEXT:    [[SUB:%.*]] = add nsw i32 [[ADD]], -5000
+; CHECK-NEXT:    [[COND:%.*]] = icmp ult i32 [[SUB]], 5000
+; CHECK-NEXT:    ret i1 [[COND]]
+;
+entry:
+  %add = add nsw i32 %a, 10000
+  %sub = add i32 %add, -5000
+  %cond = icmp ult i32 %sub, 5000
+  ret i1 %cond
+}