Vector related arith missing nsw on addition

[bcardosolopes]

If we look at how LLVM currently codegen for this, we get a add nsw instead of a plain add, see https://godbolt.org/z/xdevh38r8. There are probably other differences too.

Originally posted by @bcardosolopes in #613 (comment)

[seven-mile]

I can repro this for just scalar arith, too. See this program. I guess we are missing the corresponding logic in ScalarExprEmitter. The lowering is correct however.

clangir/clang/lib/CodeGen/CGExprScalar.cpp

Lines 4096 to 4111 in 76f7488

	if (op.Ty->isSignedIntegerOrEnumerationType()) {
	switch (CGF.getLangOpts().getSignedOverflowBehavior()) {
	case LangOptions::SOB_Defined:
	if (!CGF.SanOpts.has(SanitizerKind::SignedIntegerOverflow))
	return Builder.CreateAdd(op.LHS, op.RHS, "add");
	[[fallthrough]];
	case LangOptions::SOB_Undefined:
	if (!CGF.SanOpts.has(SanitizerKind::SignedIntegerOverflow))
	return Builder.CreateNSWAdd(op.LHS, op.RHS, "add");
	[[fallthrough]];
	case LangOptions::SOB_Trapping:
	if (CanElideOverflowCheck(CGF.getContext(), op))
	return Builder.CreateNSWAdd(op.LHS, op.RHS, "add");
	return EmitOverflowCheckedBinOp(op);
	}
	}

[mingshi2333]

I checked and it seems Subop has already done this logic, so if no one else has done it, it can be assigned to me

clangir/clang/lib/CIR/CodeGen/CIRGenExprScalar.cpp

Lines 1317 to 1338 in 9720c61

	mlir::Value ScalarExprEmitter::buildSub(const BinOpInfo &Ops) {
	// The LHS is always a pointer if either side is.
	if (!Ops.LHS.getType().isa<mlir::cir::PointerType>()) {
	if (Ops.CompType->isSignedIntegerOrEnumerationType()) {
	switch (CGF.getLangOpts().getSignedOverflowBehavior()) {
	case LangOptions::SOB_Defined: {
	if (!CGF.SanOpts.has(SanitizerKind::SignedIntegerOverflow))
	return Builder.createSub(Ops.LHS, Ops.RHS);
	[[fallthrough]];
	}
	case LangOptions::SOB_Undefined:
	if (!CGF.SanOpts.has(SanitizerKind::SignedIntegerOverflow))
	return Builder.createNSWSub(Ops.LHS, Ops.RHS);
	[[fallthrough]];
	case LangOptions::SOB_Trapping:
	if (CanElideOverflowCheck(CGF.getContext(), Ops))
	return Builder.createNSWSub(Ops.LHS, Ops.RHS);
	llvm_unreachable("NYI");
	}
	}
	if (Ops.FullType->isConstantMatrixType()) {